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See detailQuantitative Prediction of Optical Absorption in Molecular Solids from an Optimally Tuned Screened Range-Separated Hybrid Functional
Manna, Arun; Refaely-Abramson, Sivan; Reilly, Anthony et al

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

We show that fundamental gaps and optical spectra of molecular solids can be predicted quantitatively and nonempirically within the framework of time-dependent density functional theory (TDDFT) using the ... [more ▼]

We show that fundamental gaps and optical spectra of molecular solids can be predicted quantitatively and nonempirically within the framework of time-dependent density functional theory (TDDFT) using the recently developed optimally tuned screened range-separated hybrid (OT-SRSH) functional approach. In this scheme, the electronic structure of the gas-phase molecule is determined by optimal tuning of the range-separation parameter in a range-separated hybrid functional. Screening and polarization in the solid state are taken into account by adding long-range dielectric screening to the functional form, with the modified functional used to perform self-consistent periodic boundary calculations for the crystalline solid. We provide a comprehensive benchmark for the accuracy of our approach by considering the X23 set of molecular solids and comparing results obtained from TDDFT with those obtained from many-body perturbation theory in the GW-BSE approximation. We additionally compare results obtained from dielectric screening computed within the random-phase approximation to those obtained from the computationally more efficient many-body dispersion approach and find that this influences the fundamental gap but has little effect on the optical spectra. Our approach is therefore robust and can be used for studies of molecular solids that are typically beyond the reach of computationally more intensive methods. [less ▲]

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See detailTerahertz spectroscopy of 2,4,6-trinitrotoluene molecular solids from first principles
Azuri, Ido; Hirsch, Anna; Reilly, Anthony et al

in Beilstein Journal of Organic Chemistry (2018), 14

We present a computational analysis of the terahertz spectra of the monoclinic and the orthorhombic polymorphs of 2,4,6-trinitrotoluene. Very good agreement with experimental data is found when using ... [more ▼]

We present a computational analysis of the terahertz spectra of the monoclinic and the orthorhombic polymorphs of 2,4,6-trinitrotoluene. Very good agreement with experimental data is found when using density functional theory that includes Tkatchenko–Scheffler pair-wise dispersion interactions. Furthermore, we show that for these polymorphs the theoretical results are only weakly affected by many-body dispersion contributions. The absence of dispersion interactions, however, causes sizable shifts in vibrational frequencies and directly affects the spatial character of the vibrational modes. Mode assignment allows for a distinction between the contributions of the monoclinic and orthorhombic polymorphs and shows that modes in the range from 0 to ca. 3.3 THz comprise both inter- and intramolecular vibrations, with the former dominating below ca. 1.5 THz. We also find that intramolecular contributions primarily involve the nitro and methyl groups. Finally, we present a prediction for the terahertz spectrum of 1,3,5-trinitrobenzene, showing that a modest chemical change leads to a markedly different terahertz spectrum. [less ▲]

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See detailUnderstanding Molecular Crystals with Dispersion-Inclusive Density Functional Theory: Pairwise Corrections and Beyond
Kronik, Leeor; Tkatchenko, Alexandre UL

in ACCOUNTS OF CHEMICAL RESEARCH (2014), 47(11, SI), 3208-3216

Molecular crystals are ubiquitous in many areas of science and engineering, including biology and medicine. Until recently, our ability to understand and predict their structure and properties using ... [more ▼]

Molecular crystals are ubiquitous in many areas of science and engineering, including biology and medicine. Until recently, our ability to understand and predict their structure and properties using density functional theory was severely limited by the lack of approximate exchangecorrelation functionals able to achieve sufficient accuracy. Here we show that there are many cases where the simple, minimally empirical pairwise correction scheme of Tkatchenko and Scheffler provides a useful prediction of the structure and properties of molecular crystals. After a brief introduction of the approach, we demonstrate its strength through some examples taken from our recent work. First, we show the accuracy of the approach using benchmark data sets of molecular complexes. Then we show its efficacy for structural determination using the hemozoin crystal, a challenging system possessing a wide range of strong and weak binding scenarios. Next, we show that it is equally useful for response properties by considering the elastic constants exhibited by the supramolecular diphenylalanine peptide solid and the infrared signature of water libration movements in brushite. Throughout, we emphasize lessons learned not only for the methodology but also for the chemistry and physics of the crystals in question. We further show that in many other scenarios where the simple pairwise correction scheme is not sufficiently accurate, one can go beyond it by employing a computationally inexpensive many-body dispersive approach that results in useful, quantitative accuracy, even in the presence of significant screening and/or multibody contributions to the dispersive energy. We explain the principles of the many-body approach and demonstrate its accuracy for benchmark data sets of small and large molecular complexes and molecular solids. [less ▲]

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See detailPair-Wise and Many-Body Dispersive Interactions Coupled to an Optimally Tuned Range-Separated Hybrid Functional
Agrawal, Piyush; Tkatchenko, Alexandre UL; Kronik, Leeor

in JOURNAL OF CHEMICAL THEORY AND COMPUTATION (2013), 9(8), 3473-3478

We propose a nonempirical, pair-wise or many-body dispersion-corrected optimally tuned range-separated hybrid functional. This functional retains the advantages of the optimal-tuning approach in the ... [more ▼]

We propose a nonempirical, pair-wise or many-body dispersion-corrected optimally tuned range-separated hybrid functional. This functional retains the advantages of the optimal-tuning approach in the prediction of the electronic structure. At the same time, it gains accuracy in the prediction of binding energies for dispersively bound systems, as demonstrated on the S22 and S66 benchmark sets of weakly bound dimers. [less ▲]

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See detailDispersion Interactions with Density-Functional Theory: Benchmarking Semiempirical and Interatomic Pairwise Corrected Density Functionals
Marom, Noa; Tkatchenko, Alexandre UL; Rossi, Mariana et al

in JOURNAL OF CHEMICAL THEORY AND COMPUTATION (2011), 7(12), 3944-3951

We present a comparative assessment of the accuracy of two different approaches for evaluating dispersion interactions: interatomic pairwise corrections and semiempirical meta-generalized-gradient ... [more ▼]

We present a comparative assessment of the accuracy of two different approaches for evaluating dispersion interactions: interatomic pairwise corrections and semiempirical meta-generalized-gradient-approximation (meta-GGA)-based functionals. This is achieved by employing conventional (semi)local and (screened-)hybrid functionals, as well as semiempirical hybrid and nonhybrid meta-GGA functionals of the M06 family, with and without interatomic pairwise Tkatchenko Scheffler corrections. All of those are tested against the benchmark S22 set of weakly bound systems a representative larger molecular complex (dimer of NiPc molecules), and a representative dispersively bound solid (hexagonal boron nitride). For the 522 database, we also compare our results with those obtained from the pairwise correction of Grimme (DFT-D3) and nonlocal Langreth Lundqvist furtctionals (vdW-DF1 and vdW-DF2). We find that the semiempirical kinetic-energy-density dependence introduced in the M06 functionals mimics some of the nonlocal correlation needed to describe dispersion. However, long-range contributions are still missing. Pair-wise interatomic corrections, applied to conventional semilocal or hybrid functionals, or to M06 functionals, provide for a satisfactory level of accuracy irrespectively of the underlying functional. Specifically, screened-hybrid functionals such as the.Heyd Scuseria Ernzerhof (HSE) approach reduce self-interaction errors in systems possessing both localized and delocalized orbitals and can be applied to both finite and extended systems. Therefore, they serve as a useful underlying functional for dispersion corrections. [less ▲]

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