(192bc) Accurate Methods to Describe System-Specific Polarization and Dispersion Energies

We introduce several improvements to the description of polarization and dispersion energies in complex materials. First, we use DDEC6 atomic population analysis [1,2] to improve the computed r-cubed moments of atoms in diverse material types. These r-cubed moments are used as inputs to compute atomic polarizabilities and dispersion coefficients. Second, we calculate and include the conduction limit upper bound on the polarizabilities of buried atoms. This vastly improves the description of polarizabilities in solids and other dense materials. Third, we introduce improved van der Waals radii and multi-body screening radii for the frequency-dependent dipole-dipole interaction tensor used in self-consistent screening[3] to compute C6 dispersion coefficients and polarizabilities. Fourth, we separately compute and clarify the difference between polarizability due to an externally applied electric field, fluctuating polarizabilities used in the Casimir-Polder integral, and atomic polarizabilities optimized for polarizable force-fields. Fifth, we introduce a new form of the damping functional for DFT+dispersion calculations. This new damping functional implicitly includes C8 and C10 dispersion contributions. Sixth, we derive and program a more computationally efficient formulation that includes periodic boundary conditions exactly into the multi-body dispersion (MBD) equations for the range-separated coupled-fluctuating dipole model (rs-CFDM[3]). We present computational results for molecules and solids, including several benchmark sets.

[1] T. A. Manz and N. Gabaldon Limas, “Introducing DDEC6 atomic population analysis: part 1. Charge partitioning theory and methodology,” RSC Advances, 6 (2016) 47771-47801.

[2] N. Gabaldon Limas and T. A. Manz, “Introducing DDEC6 atomic population analysis: part 2. Computed results for a wide range of periodic and nonperiodic materials,” RSC Advances, 6 (2016) 45727-45747.

[3] A. Ambrosetti, A. M. Reilly, R. A. Distasio Jr., and A. Tkatchenko, “Long-range correlation energy calculated from coupled atomic response functions,” J. Chem. Phys. 140 (2014) 18A508.