4 research outputs found
Efficient Calculations of Dispersion Energies for Nanoscale Systems from Coupled Density Response Functions
Dispersion energies computed from coupled KohnâSham
(CKS)
dynamic densityâdensity 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 âdensity functional theory plus dispersionâ
approaches
Extension of the HartreeâFock Plus Dispersion Method by First-Order Correlation Effects
The HartreeâFock 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 KohnâSham 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 [CCSDTÂ(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