Efficient Calculations of Dispersion Energies for Nanoscale Systems from Coupled Density Response Functions

Dispersion energies computed from coupled Kohn–Sham (CKS) dynamic density–density response functions are known to be highly accurate. At the same time, the computational algorithm is of only modest complexity compared to other accurate methods of dispersion energy calculation. We present a new implementation of this algorithm that removes several computational barriers present in current implementations and enables calculations of dispersion energies for systems with more than 200 atoms using more than 5000 basis functions. The improvements were mainly achieved by reorganizing the algorithm to minimize memory and disk usage. We present applications to two systems: the buckycatcher complex with fullerene and the vancomycin complex with a diacetyl-Lys-d-Ala-d-Ala bacterial wall precursor, both calculations performed with triple-ζ-quality basis sets. Our implementation makes it possible to use <i>ab initio</i> computed dispersion energies in popular “density functional theory plus dispersion” approaches

Extension of the Hartree−Fock Plus Dispersion Method by First-Order Correlation Effects

The Hartree−Fock plus dispersion (HFD) method for calculations of intermolecular interaction energies has been extended by the addition of the correlation part of the first-order interaction energy computed from Kohn−Sham determinants of monomers. This extension increases the computational requirements of the HFD approach only insignificantly and at the same time reduces the uncertainties of the interaction energies several times for most of the investigated systems. Thus, the proposed method becomes an attractive computational tool for investigating interactions of very large molecules at the HF-level costs

Three-Body Nonadditive Potential for Argon with Estimated Uncertainties and Third Virial Coefficient

The three-body nonadditive interaction energy between argon atoms was calculated at 300 geometries using coupled cluster methods up to single, double, triple, and noniterative quadruple excitations [CCSDT­(Q)], and including the core correlation and relativistic effects. The uncertainty of the calculated energy was estimated at each geometry. The analytic function fitted to the energies is currently the most accurate three-body argon potential. Values of the third virial coefficient <i>C</i>(<i>T</i>) with full account of quantum effects were computed from 80 to 10000 K by a path-integral Monte Carlo method. The calculation made use of an existing high-quality pair potential [Patkowski, K.; Szalewicz, K. <i>J. Chem. Phys.</i> <b>2010</b>, <i>133</i>, 094304] and of the three-body potential derived in the present work. Uncertainties in the potential were propagated to estimate uncertainties in <i>C</i>(<i>T</i>). The results were compared with available experimental data, including some values of <i>C</i>(<i>T</i>) newly derived in this work from previously published high-accuracy density measurements. Our results are generally consistent with the available experimental data in the limited range of temperatures where data exist, but at many conditions, especially at higher temperatures, the uncertainties of our calculated values are smaller than the uncertainties of the experimental values

Ab Initio Water Pair Potential with Flexible Monomers

A potential energy surface for the water dimer with explicit dependence on monomer coordinates is presented. The surface was fitted to a set of previously published interaction energies computed on a grid of over a quarter million points in the 12-dimensional configurational space using symmetry-adapted perturbation theory and coupled-cluster methods. The present fit removes small errors in published fits, and its accuracy is critically evaluated. The minimum and saddle-point structures of the potential surface were found to be very close to predictions from direct ab initio optimizations. The computed second virial coefficients agreed well with experimental values. At low temperatures, the effects of monomer flexibility in the virial coefficients were found to be much smaller than the quantum effects