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See detailQuantum tunneling of thermal protons through pristine graphene
Poltavskyi, Igor UL; Tkatchenko, Alexandre UL; Mortazavi, Majid et al

in Journal of Chemical Physics (2018), 148(20), 204707

Engineering of atomically thin membranes for hydrogen isotope separation is an actual challenge which has a broad range of applications. Recent experiments [M. Lozada-Hidalgo et al., Science 351, 68 (2016 ... [more ▼]

Engineering of atomically thin membranes for hydrogen isotope separation is an actual challenge which has a broad range of applications. Recent experiments [M. Lozada-Hidalgo et al., Science 351, 68 (2016)] unambiguously demonstrate an order-of-magnitude difference in permeabilities of graphene-based membranes to protons and deuterons at ambient conditions, making such materials promising for novel separation technologies. Here we demonstrate that the permeability mechanism in such systems changes from quantum tunneling for protons to quasi-classical transport for heavier isotopes. Quantum nuclear effects exhibit large temperature and mass dependence, modifying the Arrhenius activation energy and Arrhenius prefactor for protons by more than 0.5 eV and by seven orders of magnitude correspondingly. Our findings not only shed light on the separation process for hydrogen isotope ions passing through pristine graphene but also offer new insights for controlling ion transport mechanisms in nanostructured separation membranes by manipulating the shape of the barrier and transport process conditions. [less ▲]

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See detailNon-covalent interactions across organic and biological subsets of chemical space: Physics-based potentials parametrized from machine learning
Bereau, Tristan; Distasio Jr., Robert A.; Tkatchenko, Alexandre UL et al

in Journal of Chemical Physics (2018), 148

Classical intermolecular potentials typically require an extensive parametrization procedure for any new compound considered. To do away with prior parametrization, we propose a combination of physics ... [more ▼]

Classical intermolecular potentials typically require an extensive parametrization procedure for any new compound considered. To do away with prior parametrization, we propose a combination of physics-based potentials with machine learning (ML), coined IPML, which is transferable across small neutral organic and biologically relevant molecules. ML models provide on-the-fly predictions for environment-dependent local atomic properties: electrostatic multipole coefficients (significant error reduction compared to previously reported), the population and decay rate of valence atomic densities, and polarizabilities across conformations and chemical compositions of H, C, N, and O atoms. These parameters enable accurate calculations of intermolecular contributions—electrostatics, charge penetration, repulsion, induction/polarization, and many-body dispersion. Unlike other potentials, this model is transferable in its ability to handle new molecules and conformations without explicit prior parametrization: All local atomic properties are predicted from ML, leaving only eight global parameters—optimized once and for all across compounds.We validate IPML on various gasphase dimers at and away from equilibrium separation, where we obtain mean absolute errors between 0.4 and 0.7 kcal/mol for several chemically and conformationally diverse datasets representative of non-covalent interactions in biologically relevant molecules. We further focus on hydrogen-bonded complexes—essential but challenging due to their directional nature—where datasets of DNA base pairs and amino acids yield an extremely encouraging 1.4 kcal/mol error. Finally, and as a first look, we consider IPML for denser systems: water clusters, supramolecular host-guest complexes, and the benzene crystal. [less ▲]

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See detailPerturbed path integrals in imaginary time: Efficiently modeling nuclear quantum effects in molecules and materials
Poltavskyi, Igor UL; DiStasio, Robert; Tkatchenko, Alexandre UL

in Journal of Chemical Physics (2018), 148(10), 102325

Nuclear quantum effects (NQE), which include both zero-point motion and tunneling, exhibit quite an impressive range of influence over the equilibrium and dynamical properties of molecules and materials ... [more ▼]

Nuclear quantum effects (NQE), which include both zero-point motion and tunneling, exhibit quite an impressive range of influence over the equilibrium and dynamical properties of molecules and materials. In this work, we extend our recently proposed perturbed path-integral (PPI) approach for modeling NQE in molecular systems [I. Poltavsky and A. Tkatchenko, Chem. Sci. 7, 1368 (2016)], which successfully combines the advantages of thermodynamic perturbation theory with path-integral molecular dynamics (PIMD), in a number of important directions. First, we demonstrate the accuracy, performance, and general applicability of the PPI approach to both molecules and extended (condensed-phase) materials. Second, we derive a series of estimators within the PPI approach to enable calculations of structural properties such as radial distribution functions (RDFs) that exhibit rapid convergence with respect to the number of beads in the PIMD simulation. Finally, we introduce an effective nuclear temperature formalism within the framework of the PPI approach and demonstrate that such effective temperatures can be an extremely useful tool in quantitatively estimating the “quantumness” associated with different degrees of freedom in the system as well as providing a reliable quantitative assessment of the convergence of PIMD simulations. Since the PPI approach only requires the use of standard second-order imaginary-time PIMD simulations, these developments enable one to include a treatment of NQE in equilibrium thermodynamic properties (such as energies, heat capacities, and RDFs) with the accuracy of higher-order methods but at a fraction of the computational cost, thereby enabling first-principles modeling that simultaneously accounts for the quantum mechanical nature of both electrons and nuclei in large-scale molecules and materials. [less ▲]

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See detailSchNet – A deep learning architecture for molecules and materials
Schütt, Kristof T.; Sauceda, Huziel E.; Kindermans, P. J. et al

in Journal of Chemical Physics (2018), 148

Deep learning has led to a paradigm shift in artificial intelligence, including web, text, and image search, speech recognition, as well as bioinformatics, with growing impact in chemical physics. Machine ... [more ▼]

Deep learning has led to a paradigm shift in artificial intelligence, including web, text, and image search, speech recognition, as well as bioinformatics, with growing impact in chemical physics. Machine learning, in general, and deep learning, in particular, are ideally suitable for representing quantum-mechanical interactions, enabling us to model nonlinear potential-energy surfaces or enhancing the exploration of chemical compound space. Here we present the deep learning architecture SchNet that is specifically designed to model atomistic systems by making use of continuous-filter convolutional layers. We demonstrate the capabilities of SchNet by accurately predicting a range of properties across chemical space for molecules and materials, where our model learns chemically plausible embeddings of atom types across the periodic table. Finally, we employ SchNet to predict potential-energy surfaces and energy-conserving force fields for molecular dynamics simulations of small molecules and perform an exemplary study on the quantum-mechanical properties of C20- fullerene that would have been infeasible with regular ab initio molecular dynamics. [less ▲]

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See detailFast and accurate quantum Monte Carlo for molecular crystals
Zen, Andrea; Brandenburg, Jan Gerit; Klimes, Jiri et al

in Proceedings of the National Academy of Sciences of the United States of America (2018), 115

Computer simulation plays a central role in modern-day materials science. The utility of a given computational approach depends largely on the balance it provides between accuracy and computational cost ... [more ▼]

Computer simulation plays a central role in modern-day materials science. The utility of a given computational approach depends largely on the balance it provides between accuracy and computational cost. Molecular crystals are a class of materials of great technological importance which are challenging for even the most sophisticated ab initio electronic structure theories to accurately describe. This is partly because they are held together by a balance of weak intermolecular forces but also because the primitive cells of molecular crystals are often substantially larger than those of atomic solids. Here, we demonstrate that diffusion quantum Monte Carlo (DMC) delivers subchemical accuracy for a diverse set of molecular crystals at a surprisingly moderate computational cost. As such, we anticipate that DMC can play an important role in understanding and predicting the properties of a large number of molecular crystals, including those built from relatively large molecules which are far beyond reach of other high-accuracy methods. [less ▲]

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See detailElectronic Exchange and Correlation in van der Waals Systems: Balancing Semilocal and Nonlocal Energy Contributions
Hermann, Jan UL; Tkatchenko, Alexandre UL

in Journal of Chemical Theory and Computation (2018), 14

Short-range correlations in motion of electrons in matter are captured well by semilocal exchange−correlation (XC) functionals in density functional theory (DFT), but long-range correlations are neglected ... [more ▼]

Short-range correlations in motion of electrons in matter are captured well by semilocal exchange−correlation (XC) functionals in density functional theory (DFT), but long-range correlations are neglected in such models and must be treated by van der Waals (vdW) dispersion methods. Whereas the effective range of distances at which fluctuations are correlated is usually explicit in the vdW models, the complementary range of semilocal functionals can be observed only implicitly, requiring an introduction of empirical damping functions to couple the semilocal and nonlocal contributions to the XC energy. We present a comprehensive study of the interplay between these short-range and long-range energy contributions in eight semilocal functionals (LDA, PBE, TPSS, SCAN, PBE0, B3LYP, SCAN0, M06-L) and three vdW models (MBD, D3, VV10) on noncovalently bonded organic dimers (S66×8), molecular crystals (X23), and supramolecular complexes (S12L), as well as on a series of graphene-flake dimers, covering a range of intermolecular distances and binding energies (0.5−130 kcal/mol). The binding-energy profiles of many of the DFT+vdW combinations differ both quantitatively and qualitatively, and some of the qualitative differences are independent of the choice of the vdW model, establishing them as intrinsic properties of the respective semilocal functionals. We find that while the SCAN+vdW method yields a narrow range of binding-energy errors, the effective range of SCAN depends on system size, and we link this behavior to the specific dependence of SCAN on the electron localization function α around α = 1. Our study provides a systematic procedure to evaluate the consistency of semilocal XC functionals when paired with nonlocal vdW models and leads us to conclude that nonempirical generalized-gradient and hybrid functionals are currently among the most balanced semilocal choices for vdW systems. [less ▲]

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See detailModeling Nonreactive Molecule−Surface Systems on Experimentally Relevant Time and Length Scales: Dynamics and Conductance of Polyfluorene on Au(111)
Li, Zhi; Tkatchenko, Alexandre UL; Franco, Ignacio

in Journal of Physical Chemistry Letters (2018), 9

We propose a computationally efficient strategy to accurately model nonreactive molecule−surface interactions that adapts density functional theory calculations with the Tkatchenko−Scheffler scheme for ... [more ▼]

We propose a computationally efficient strategy to accurately model nonreactive molecule−surface interactions that adapts density functional theory calculations with the Tkatchenko−Scheffler scheme for van der Waals interactions into a simple classical force field. The resulting force field requires just two adjustable parameters per atom type that are needed to capture short-range and polarization interactions. The developed strategy allows for classical molecular dynamics simulation of molecules on surfaces with the accuracy of highlevel electronic structure methods but for system sizes (103 to 107 atoms) and timescales (picoseconds to microseconds) that go well beyond what can be achieved with first-principles methods. Parameters for H, sp2 C, and O on Au(111) are developed and employed to atomistically model experiments that measure the conductance of a single polyfluorene on Au(111) as a continuous function of its length. The simulations qualitatively capture both the gross and fine features of the observed conductance decay during initial junction elongation and lead to a revised atomistic understanding of the experiment. [less ▲]

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See detailStructure and Stability of Molecular Crystals with Many-Body Dispersion-Inclusive Density Functional Tight Binding
Mortazavi, Majid; Brandenburg, Jan Gerit; Maurer, Reinhard J. et al

in Journal of Physical Chemistry Letters (2018), 9

Accurate prediction of structure and stability of molecular crystals is crucial in materials science and requires reliable modeling of long-range dispersion interactions. Semiempirical electronic ... [more ▼]

Accurate prediction of structure and stability of molecular crystals is crucial in materials science and requires reliable modeling of long-range dispersion interactions. Semiempirical electronic structure methods are computationally more efficient than their ab initio counterparts, allowing structure sampling with significant speedups. We combine the Tkatchenko−Scheffler van der Waals method (TS) and the many-body dispersion method (MBD) with third-order density functional tight-binding (DFTB3) via a charge population-based method. We find an overall good performance for the X23 benchmark database of molecular crystals, despite an underestimation of crystal volume that can be traced to the DFTB parametrization. We achieve accurate lattice energy predictions with DFT+MBD energetics on top of vdW-inclusive DFTB3 structures, resulting in a speedup of up to 3000 times compared with a full DFT treatment. This suggests that vdW-inclusive DFTB3 can serve as a viable structural prescreening tool in crystal structure prediction. [less ▲]

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See detailUniaxial negative thermal expansion and metallophilicity in Cu3[Co(CN)6]
Sapnik, A. F.; Liu, X.; Böstrom, H. L. B. et al

in Journal of Solid State Chemistry (2018), 258

We report the synthesis and structural characterisation of the molecular framework copper(I) hexacyanocobaltate(III), Cu3[Co(CN)6], which we find to be isostructural to H3[Co(CN)6] and the colossal ... [more ▼]

We report the synthesis and structural characterisation of the molecular framework copper(I) hexacyanocobaltate(III), Cu3[Co(CN)6], which we find to be isostructural to H3[Co(CN)6] and the colossal negative thermal expansion material Ag3[Co(CN)6]. Using synchrotron X-ray powder diffraction measurements, we find strong positive and negative thermal expansion behaviour respectively perpendicular and parallel to the trigonal crystal axis: α = 25.4(5) MK a −1 and α = − 43.5(8) MK c −1. These opposing effects collectively result in a volume expansivity α = 7.4(11) MK V −1 that is remarkably small for an anisotropic molecular framework. This thermal response is discussed in the context of the behaviour of the analogous H- and Ag-containing systems. We make use of density-functional theory with many-body dispersion interactions (DFT + MBD) to demonstrate that Cu+…Cu+ metallophilic (‘cuprophilic’) interactions are significantly weaker in Cu3[Co(CN)6] than Ag+…Ag+ interactions in Ag3[Co(CN)6], but that this lowering of energy scale counterintuitively translates to a more moderate—rather than enhanced—degree of structural flexibility. The same conclusion is drawn from consideration of a simple GULP model, which we also present here. Our results demonstrate that strong interactions can actually be exploited in the design of ultra-responsive materials if those interactions are set up to act in tension. [less ▲]

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See detailHidden Beneath the Surface: Origin of the Observed Enantioselective Adsorption on PdGa(111)
Yakutovich, Aliaksandr V.; Hoja, Johannes UL; Passerone, Daniele et al

in Journal of the American Chemical Society (2018), 140(4), 1401-1408

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See detailSchNet: A continuous-filter convolutional neural network for modeling quantum interactions
Schütt, Kristof T.; Kindermans, P. J.; Sauceda, Huziel E. et al

in 31st Conference on Neural Information Processing Systems (NIPS 2017), Long Beach, CA, USA (2017, December)

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See detailEffective scheme to determine accurate defect formation energies and charge transition levels of point defects in semiconductors
Yao, Cang Lang; Li, Jian Chen; Gao, Wang et al

in Physical Review. B : Solid State (2017), 96

We propose an effective method to accurately determine the defect formation energy Ef and charge transition level ε of the point defects using exclusively cohesive energy Ecoh and the fundamental band gap ... [more ▼]

We propose an effective method to accurately determine the defect formation energy Ef and charge transition level ε of the point defects using exclusively cohesive energy Ecoh and the fundamental band gap Eg of pristine host materials. We find that Ef of the point defects can be effectively separated into geometric and electronic contributions with a functional form: Ef = χEcoh + λEg, where χ and λ are dictated by the geometric and electronic factors of the point defects (χ and λ are defect dependent). Such a linear combination of Ecoh and Eg reproduces Ef with an accuracy better than 5% for electronic structure methods ranging from hybrid densityfunctional theory (DFT) to many-body random-phase approximation (RPA) and experiments. Accordingly, ε is also determined by Ecoh/Eg and the defect geometric/electronic factors. The identified correlation is rather general for monovacancies and interstitials, which holds in a wide variety of semiconductors covering Si, Ge, phosphorenes, ZnO, GaAs, and InP, and enables one to obtain reliable values of Ef and ε of the point defects for RPA and experiments based on semilocal DFT calculations. [less ▲]

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See detailFirst-Principles Study of Alkoxides Adsorbed on Au(111) and Au(110) Surfaces: Assessing the Roles of Noncovalent Interactions and Molecular Structures in Catalysis
Cheenicode Kabeer, Fairoja; Chen, Wei; Madix, Robert J. et al

in Journal of Physical Chemistry C (2017), 121

Microscopic understanding of molecular adsorption on catalytic surfaces is crucial for controlling the activity and selectivity of chemical reactions. However, for complex molecules, the adsorption ... [more ▼]

Microscopic understanding of molecular adsorption on catalytic surfaces is crucial for controlling the activity and selectivity of chemical reactions. However, for complex molecules, the adsorption process is very systemspecific and there is a clear need to elaborate systematic understanding of important factors that determine catalytic functionality. Here, we investigate the binding of eight molecules, including seven alkoxides and one carboxylate, on the Au(111) and Au(110) surfaces. Our density-functional theory calculations including long-range van der Waals interactions demonstrate the significant role of these “weak” noncovalent forces on the adsorption structures, energetics, and relative adsorbate stabilities. Interestingly, the binding energy trends are insensitive to the surface structure. Instead, the adsorption stability depends strongly on the structural and chemical characteristics of the molecules: linear vs branching configurations, number of unsaturated C−C bonds, bidentate adsorption, and the presence of electronegative atoms. Our calculations help establish the influence of individual and collective chemical factors that determine the catalytic selectivity of alkoxides. [less ▲]

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See detailElectronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions
Ferri, Nicola; Ambrosetti, Alberto; Tkatchenko, Alexandre UL

in Physical Review Materials (2017), 1(1), 026003

Electronic charge rearrangements at interfaces between organic molecules and solid surfaces play a key role in a wide range of applications in catalysis, light-emitting diodes, single-molecule junctions ... [more ▼]

Electronic charge rearrangements at interfaces between organic molecules and solid surfaces play a key role in a wide range of applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. It is common to utilize electrostatics and Pauli pushback to control the interface electronic properties, while the ubiquitous van der Waals (vdW) interactions are often considered to have a negligible direct contribution (beyond the obvious structural relaxation). Here, we apply a fully self-consistent Tkatchenko-Scheffler vdW density functional to demonstrate that the weak vdW interactions can induce sizable charge rearrangements at hybrid metal/organic systems (HMOS). The complex vdW correlation potential smears out the interfacial electronic density, thereby reducing the charge transfer in HMOS, changes the interface work functions by up to 0.2 eV, and increases the interface dipole moment by up to 0.3 Debye. Our results suggest that vdW interactions should be considered as an additional control parameter in the design of hybrid interfaces with the desired electronic properties. [less ▲]

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See detailCatalysis beyond frontier molecular orbitals: Selectivity in partial hydrogenation of multi-unsaturated hydrocarbons on metal catalysts
Liu, Wei; Jiang, Yingda; Dostert, Karl-Heinz et al

in Science Advances (2017), 3

The mechanistic understanding and control over transformations of multi-unsaturated hydrocarbons on transition metal surfaces remains one of the major challenges of hydrogenation catalysis. To reveal the ... [more ▼]

The mechanistic understanding and control over transformations of multi-unsaturated hydrocarbons on transition metal surfaces remains one of the major challenges of hydrogenation catalysis. To reveal the microscopic origins of hydrogenation chemoselectivity, we performed a comprehensive theoretical investigation on the reactivity of two a,b-unsaturated carbonyls—isophorone and acrolein—on seven (111) metal surfaces: Pd, Pt, Rh, Ir, Cu, Ag, and Au. In doing so, we uncover a general mechanism that goes beyond the celebrated frontier molecular orbital theory, rationalizing the C--C bond activation in isophorone and acrolein as a result of significant surface-induced broadening of high-energy inner molecular orbitals. By extending our calculations to hydrogen-precovered surface and higher adsorbate surface coverage, we further confirm the validity of the “inner orbital broadening mechanism” under realistic catalytic conditions. The proposed mechanism is fully supported by our experimental reaction studies for isophorone and acrolein over Pd nanoparticles terminated with (111) facets. Although the position of the frontier molecular orbitals in these molecules, which are commonly considered to be responsible for chemical interactions, suggests preferential hydrogenation of the C--O double bond, experiments show that hydrogenation occurs at the C--C bond on Pd catalysts. The extent of broadening of inner molecular orbitals might be used as a guiding principle to predict the chemoselectivity for a wide class of catalytic reactions at metal surfaces. [less ▲]

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See detailProperties of the water to boron nitride interaction: from zero to two dimensions with benchmark accuracy
Al-Hamdani, Yasmine UL; Rossi, Mariana; Alfè, Dario et al

in Journal of Chemical Physics (2017), 147

Molecular adsorption on surfaces plays an important part in catalysis, corrosion, desalination, and various other processes that are relevant to industry and in nature. As a complement to experiments ... [more ▼]

Molecular adsorption on surfaces plays an important part in catalysis, corrosion, desalination, and various other processes that are relevant to industry and in nature. As a complement to experiments, accurate adsorption energies can be obtained using various sophisticated electronic structure methods that can now be applied to periodic systems. The adsorption energy of water on boron nitride substrates, going from zero to 2-dimensional periodicity, is particularly interesting as it calls for an accurate treatment of polarizable electrostatics and dispersion interactions, as well as posing a practical challenge to experiments and electronic structure methods. Here, we present reference adsorption energies, static polarizabilities, and dynamic polarizabilities, for water on BN substrates of varying size and dimension. Adsorption energies are computed with coupled cluster theory, fixed-node quantum Monte Carlo (FNQMC), the random phase approximation, and second order Møller-Plesset theory. These wavefunction based correlated methods are found to agree in molecular as well as periodic systems. The best estimate of the water/h-BN adsorption energy is −107 ± 7 meV from FNQMC. In addition, the water adsorption energy on the BN substrates could be expected to grow monotonically with the size of the substrate due to increased dispersion interactions, but interestingly, this is not the case here. This peculiar finding is explained using the static polarizabilities and molecular dispersion coefficients of the systems, as computed from time-dependent density functional theory (DFT). Dynamic as well as static polarizabilities are found to be highly anisotropic in these systems. In addition, the many-body dispersion method in DFT emerges as a particularly useful estimation of finite size effects for other expensive, many-body wavefunction based methods. [less ▲]

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See detailLong-Range Repulsion Between Spatially Confined van der Waals Dimers
Sadhukhan, Mainak UL; Tkatchenko, Alexandre UL

in Physical Review Letters (2017), 118

It is an undisputed textbook fact that nonretarded van der Waals (vdW) interactions between isotropic dimers are attractive, regardless of the polarizability of the interacting systems or spatial ... [more ▼]

It is an undisputed textbook fact that nonretarded van der Waals (vdW) interactions between isotropic dimers are attractive, regardless of the polarizability of the interacting systems or spatial dimensionality. The universality of vdW attraction is attributed to the dipolar coupling between fluctuating electron charge densities. Here, we demonstrate that the long-range interaction between spatially confined vdW dimers becomes repulsive when accounting for the full Coulomb interaction between charge fluctuations. Our analytic results are obtained by using the Coulomb potential as a perturbation over dipole-correlated states for two quantum harmonic oscillators embedded in spaces with reduced dimensionality; however, the long-range repulsion is expected to be a general phenomenon for spatially confined quantum systems. We suggest optical experiments to test our predictions, analyze their relevance in the context of intermolecular interactions in nanoscale environments, and rationalize the recent observation of anomalously strong screening of the lateral vdW interactions between aromatic hydrocarbons adsorbed on metal surfaces. [less ▲]

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See detailNanoscale $\uppi$\textendash$\uppi$ stacked molecules are bound by collective charge fluctuations
Hermann, Jan; Alfè, Dario; Tkatchenko, Alexandre UL

in Nature Communications (2017), 8

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See detailFirst-Principles Models for van der Waals Interactions in Molecules and Materials: Concepts, Theory, and Applications
Hermann, Jan; DiStasio Jr.; Tkatchenko, Alexandre UL

in Chemical Reviews (2017), 117

Noncovalent van der Waals (vdW) or dispersion forces are ubiquitous in nature and influence the structure, stability, dynamics, and function of molecules and materials throughout chemistry, biology ... [more ▼]

Noncovalent van der Waals (vdW) or dispersion forces are ubiquitous in nature and influence the structure, stability, dynamics, and function of molecules and materials throughout chemistry, biology, physics, and materials science. These forces are quantum mechanical in origin and arise from electrostatic interactions between fluctuations in the electronic charge density. Here, we explore the conceptual and mathematical ingredients required for an exact treatment of vdW interactions, and present a systematic and unified framework for classifying the current first-principles vdW methods based on the adiabatic-connection fluctuation−dissipation (ACFD) theorem (namely the Rutgers−Chalmers vdW-DF, Vydrov−Van Voorhis (VV), exchange-hole dipole moment (XDM), Tkatchenko−Scheffler (TS), many-body dispersion (MBD), and random-phase approximation (RPA) approaches). Particular attention is paid to the intriguing nature of many-body vdW interactions, whose fundamental relevance has recently been highlighted in several landmark experiments. The performance of these models in predicting binding energetics as well as structural, electronic, and thermodynamic properties is connected with the theoretical concepts and provides a numerical summary of the state-of-the-art in the field. We conclude with a roadmap of the conceptual, methodological, practical, and numerical challenges that remain in obtaining a universally applicable and truly predictive vdW method for realistic molecular systems and materials. [less ▲]

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See detailPhysical adsorption at the nanoscale: Towards controllable scaling of the substrate-adsorbate van der Waals interaction
Ambrosetti, Alberto; Silvestrelli, Pier Luigi; Tkatchenko, Alexandre UL

in Physical Review. B : Condensed Matter (2017), 95(1), 235417

The Lifshitz-Zaremba-Kohn (LZK) theory is commonly considered as the correct large-distance limit for the van der Waals (vdW) interaction of adsorbates (atoms, molecules, or nanoparticles) with solid ... [more ▼]

The Lifshitz-Zaremba-Kohn (LZK) theory is commonly considered as the correct large-distance limit for the van der Waals (vdW) interaction of adsorbates (atoms, molecules, or nanoparticles) with solid substrates. In the standard approximate form, implicitly based on local dielectric functions, the LZK approach predicts universal power laws for vdW interactions depending only on the dimensionality of the interacting objects. However, recent experimental findings are challenging the universality of this theoretical approach at finite distances of relevance for nanoscale assembly. Here, we present a combined analytical and numerical many-body study demonstrating that physical adsorption can be significantly enhanced at the nanoscale. Regardless of the band gap or the nature of the adsorbate specie, we find deviations from conventional LZK power laws that extend to separation distances of up to 10–20 nm. Comparison with recent experimental observations of ultra-long-ranged vdW interactions in the delamination of graphene from a silicon substrate reveals qualitative agreement with the present theory. The sensitivity of vdW interactions to the substrate response and to the adsorbate characteristic excitation frequency also suggests that adsorption strength can be effectively tuned in experiments, paving the way to an improved control of physical adsorption at the nanoscale. [less ▲]

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