The dispersion interaction between quantum mechanics and effective fragment potential molecules

Abstract

A method for calculating the dispersion energy between molecules modeled with the general effective fragment potential (EFP2) method and those modeled using a full quantum mechanics (QM) method, e.g., Hartree-Fock (HF) or second-order perturbation theory, is presented. C 6 dispersion coefficients are calculated for pairs of orbitals using dynamic polarizabilities from the EFP2 portion, and dipole integrals and orbital energies from the QM portion of the system. Dividing by the sixth power of the distance between localized molecular orbital centroids yields the first term in the commonly employed London series expansion. A C 8 term is estimated from the C 6 term to achieve closer agreement with symmetry adapted perturbation theory values. Two damping functions for the dispersion energy are evaluated. By using terms that are already computed during an ordinary HF or EFP2 calculation, the new method enables accurate and extremely rapid evaluation of the dispersioninteraction between EFP2 and QM molecules. The dispersion interaction between quantum mechanics and effective fragment potential molecules Quentin A. Smith, 1 Klaus Ruedenberg, 1 Mark S. Gordon, 1,a) and Lyudmila V. Slipchenko 2,a) A method for calculating the dispersion energy between molecules modeled with the general effective fragment potential (EFP2) method and those modeled using a full quantum mechanics (QM) method, e.g., Hartree-Fock (HF) or second-order perturbation theory, is presented. C 6 dispersion coefficients are calculated for pairs of orbitals using dynamic polarizabilities from the EFP2 portion, and dipole integrals and orbital energies from the QM portion of the system. Dividing by the sixth power of the distance between localized molecular orbital centroids yields the first term in the commonly employed London series expansion. A C 8 term is estimated from the C 6 term to achieve closer agreement with symmetry adapted perturbation theory values. Two damping functions for the dispersion energy are evaluated. By using terms that are already computed during an ordinary HF or EFP2 calculation, the new method enables accurate and extremely rapid evaluation of the dispersion interaction between EFP2 and QM molecules.

LIBEFP: A new parallel implementation of the effective fragment potential method as a portable software library

“…Currently there is an ongoing work to develop exchange‐repulsion and dispersion QM/EFP interaction terms . As soon as development of both energy and gradients is completed these terms will be enabled in the libefp package.…”

“…Additionally, the induced dipoles on the fragments are affected by the wavefunction and nuclei from the quantum part so that they need to be updated self‐consistently during the quantum self‐consistent field (SCF) procedure. In future, we plan to extend the library to provide contributions to the quantum Hamiltonian due to dispersion and exchange‐repulsion EFP terms, following the emerging developments of these terms …”

Density functional Theory Based Generalized Effective Fragment Potential Method (Postprint)

“…The method has been described in detail previously. 8,9 The D3 dispersion potential is calculated as 13,28…”

“…3,6,7 The HF based EFP2 extension with dispersion between fragments 8 or HF-EFP2 9 systems is a more general and parameter-free method for any molecular species. [8][9][10][11][12] However, the EFP1-DFT 7 potential was fitted using the B3LYP functional, which lacks long-range and dispersion interactions. The EFP1-HF 3 method was fitted to reproduce results for HF, which does not include the important electron correlation effects.…”

“…The dispersion interactions for QM systems with EFP for HF-EFP2 practically require a separated treatment for the QM part calculated with dipole integrals and orbital energies. 9 In this work, we implemented and evaluated the accuracy of the DFT-EFP2 potential, using the mean unsigned errors (MUE) and mean signed errors (MSE), relative to a number of benchmarks from the coupled cluster (CC) method with singles, doubles (CCSD) and noniterative triples with the extrapolation to the complete basis set limit (CCSD(T)/CBS). [14][15][16][17][18] The paper is organized as follows.…”