Dependence of dispersion coefficients on atomic environment

Johnson, Erin R.

doi:10.1063/1.3670015

Cited by 36 publications

(33 citation statements)

References 56 publications

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“…This is done in the DFT‐D3 method, where the fixed dispersion coefficients were replaced by coefficients dependent on atomic coordination. Another important dispersion model is the exchange‐dipole moment (XDM) model, which is also density dependent and includes pairwise interactions up to quadrupole–quadrupole interactions.…”

Section: Calculating Crystal Structures and Lattice Energiesmentioning

confidence: 99%

First‐principles modeling of molecular crystals: structures and stabilities, temperature and pressure

Hoja

Reilly

Tkatchenko

2016

WIREs Comput Mol Sci

155

222

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The understanding of the structure, stability, and response properties of molecular crystals at finite temperature and pressure is crucial for the field of crystal engineering and their application. For a long time, the field of crystal-structure prediction and modeling of molecular crystals has been dominated by classical mechanistic force-field methods. However, due to increasing computational power and the development of more sophisticated quantum-mechanical approximations, first-principles approaches based on density functional theory can now be applied to practically relevant molecular crystals. The broad transferability of first-principles methods is especially imperative for polymorphic molecular crystals. This review highlights the current status of modeling molecular crystals from first principles. We give an overview of current state-of-the-art approaches and discuss in detail the main challenges and necessary approximations. So far, the main focus in this field has been on calculating stabilities and structures without considering thermal contributions. We discuss techniques that allow one to include thermal effects at a first-principles level in the harmonic or quasi-harmonic approximation, and that are already applicable to realistic systems, or will be in the near future. Furthermore, this review also discusses how to calculate vibrational and elastic properties. Finally, we present a perspective on future uses of first-principles calculations for modeling molecular crystals and summarize the many remaining challenges in this field

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Section: Calculating Crystal Structures and Lattice Energiesmentioning

confidence: 99%

First‐principles modeling of molecular crystals: structures and stabilities, temperature and pressure

Hoja

Reilly

Tkatchenko

2016

WIREs Comput Mol Sci

155

222

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“…For sulfur, results for the II and IV oxidation states will be considered separately due to the large effect of oxidation state on C 6 dispersion coefficients. 23 The average XDM dispersion coefficient for S(II) atoms is 91.8 a.u. and the standard deviation is 2.6 a.u.…”

Section: Sulfurmentioning

confidence: 99%

“…Because the dispersion coefficients are calculated directly from properties of the electron density, they vary with the local chemical environment of each atom within a molecule or solid. 15,16,23 Higher-order C 8 and C 10 dispersion coefficients can similarly be obtained in terms of higher-order exchange-hole moment integrals. 21,22 The molecular C 6 coefficient can be expressed simply as a sum of the atomic dispersion coefficients for all pairs of atoms within the molecule:…”

Section: Introductionmentioning

confidence: 99%

“…This suggests that, for organic compounds, variations in the chemical environment of an atom do not drastically affect the strength of its dispersion interactions (although this is not the case for metals15 and for changing oxidation states23 ). Thus, physically-realistic force fields should only have moderate deviations from the average dispersion coefficient for each element.…”

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confidence: 99%

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Evaluating Force-Field London Dispersion Coefficients Using the Exchange-Hole Dipole Moment Model

Mohebifar

Johnson

Rowley

2017

J. Chem. Theory Comput.

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London dispersion interactions play an integral role in materials science and biophysics. Force fields for atomistic molecular simulations typically represent dispersion interactions by the 12-6 Lennard-Jones potential using empirically determined parameters. These parameters are generally underdetermined, and there is no straightforward way to test if they are physically realistic. Alternatively, the exchange-hole dipole moment (XDM) model from density-functional theory predicts atomic and molecular London dispersion coefficients from first principles, providing an innovative strategy to validate the dispersion terms of molecular-mechanical force fields. In this work, the XDM model was used to obtain the London dispersion coefficients of 88 organic molecules relevant to biochemistry and pharmaceutical chemistry and the values compared with those derived from the Lennard-Jones parameters of the CGenFF, GAFF, OPLS, and Drude polarizable force fields. The molecular dispersion coefficients for the CGenFF, GAFF, and OPLS models are systematically higher than the XDM-calculated values by a factor of roughly 1.5, likely due to neglect of higher order dispersion terms and premature truncation of the dispersion-energy summation. The XDM dispersion coefficients span a large range for some molecular-mechanical atom types, suggesting an unrecognized source of error in force-field models, which assume that atoms of the same type have the same dispersion interactions. Agreement with the XDM dispersion coefficients is even poorer for the Drude polarizable force field. Popular water models were also examined, and TIP3P was found to have dispersion coefficients similar to the experimental and XDM references, although other models employ anomalously high values. Finally, XDM-derived dispersion coefficients were used to parametrize molecular-mechanical force fields for five liquids-benzene, toluene, cyclohexane, n-pentane, and n-hexane-which resulted in improved accuracy in the computed enthalpies of vaporization despite only having to evaluate a much smaller section of the parameter space.

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“…126 A study of the variation of the coefficients on the chemical environment for selected examples has been presented by Johnson. 155 As an illustration, the C 6 values for carbon in different hybridization states are shown in Table II. All variable-coefficient methods predict the same trend, and roughly agree in the values.…”

Section: The Hole Depletes Exactly One Electronmentioning

confidence: 99%