4,825 research outputs found
Some Observations on the Performance of the Most Recent Exchange-Correlation Functionals for the Large and Chemically Diverse GMTKN55 Benchmark
Benchmarks that span a broad swath of chemical space, such as GMTKN55, are
very useful for assessing progress in the quest for more universal DFT
functionals. We find that the WTMAD2 metrics for a great number of functionals
show a clear "Jacob's Ladder hierarchy"; that the "combinatorial" development
strategy of Head-Gordon and coworkers generates "best on rung" performers; that
the quality of the nonlocal dispersion correction becomes more important as
functionals become more accurate for nondispersion properties; that fitting
against small, unrepresentative benchmark sets leads to underperforming
functionals; and that {\omega}B97M(2) is currently the best DFT functional of
any kind, but that revDSD-D4 functionals are able to reach similar performance
using fewer parameters, and that revDOD-D4 in addition permits reduced-scaling
algorithms. If one seeks a range-separated hybrid (RSH) GGA that also performs
well for optical excitation energies, CAM-QTP-01 may be a viable option. The D4
dispersion model, with its partial charge dependence, appears to be clearly
superior to D3BJ and even possibly NL. Should one require a double hybrid
without dispersion model, noDispSD-SCAN is a viable option. Performance for the
MOBH35 transition metal benchmark is different: the best double hybrids are
competitive but not superior to {\omega}B97M-V, which offers the best
performance compromise for mixed main group-transition metal problems.Comment: 5 pages (ICCMSE-2019 conference proceedings), AIP Conference
Proceedings, in pres
Self-Organized Dynamical Equilibrium in the Corrosion of Random Solids
Self-organized criticality is characterized by power law correlations in the
non-equilibrium steady state of externally driven systems. A dynamical system
proposed here self-organizes itself to a critical state with no characteristic
size at ``dynamical equilibrium''. The system is a random solid in contact with
an aqueous solution and the dynamics is the chemical reaction of corrosion or
dissolution of the solid in the solution. The initial difference in chemical
potential at the solid-liquid interface provides the driving force. During time
evolution, the system undergoes two transitions, roughening and
anti-percolation. Finally, the system evolves to a dynamical equilibrium state
characterized by constant chemical potential and average cluster size. The
cluster size distribution exhibits power law at the final equilibrium state.Comment: 11 pages, 5 figure
Does GLPT2 Offer Any Actual Benefit Over Conventional HF-MP2 In the Context of Double-Hybrid Density Functionals?
While the inclusion of the nonlocal correlation in fifth rung "double hybrid"
functionals is definitely beneficial, one might rightfully ask whether its
evaluation in the basis of Kohn-Sham (KS) orbitals has additional value
compared to the use of Hartree-Fock reference orbitals (in a type of multilevel
scheme). We have investigated this question for a very large and chemically
diverse dataset, GMTKN55. We conclude that KS reference orbitals are
undoubtedly beneficial, but the benefit is not as large as one might
intuitively expect.Comment: 4 pages, AIP Conference Proceedings, in press (ICCMSE-2021
Performance of Localized-Orbital Coupled Cluster Approaches for the Conformational Energies of Longer n-alkane Chains
We report an update and enhancement of the ACONFL (conformer energies of
large alkanes [Ehlert, S.; Grimme, S.; Hansen, A. J. Phys. Chem. A 2022, 126,
3521-3535]) dataset. For the ACONF12 (n-dodecane) subset, we report basis set
limit canonical CCSD(T) reference data obtained from MP2-F12/cc-pV{T,Q}Z-F12
extrapolation, [CCSD(F12*)-MP2-F12]/aug-cc-pVTZ-F12, and a (T) correction from
conventional CCSD(T)/aug-cc-pV{D,T}Z calculations. Then we explored the
performance of a variety of single and composite localized-orbital CCSD(T)
approximations, ultimately finding an affordable LNO-CCSD(T)-based post-MP2
correction that agrees to 0.008 kcal/mol MAD (mean absolute deviation) with the
revised canonical reference data. In tandem with canonical MP2-F12/CBS
extrapolation, this was then used to re-evaluate the ACONF16 and ACONF20
subsets for n-hexadecane and n-icosane, respectively. A revised ACONFL set was
thus obtained. It was then used to assess the performance of different
localized-orbital coupled cluster approaches, such as PNO-LCCSD(T) as
implemented in MOLPRO, DLPNO-CCSD (T1) as implemented in ORCA, and LNO-CCSD(T)
as implemented in MRCC, at their various accuracy settings. A three-tier
LNO-CCSD(T)-based composite scheme disagrees by only 0.02 kcal/mol from the
revised ACONFL reference data. When extrapolated to the complete PNO space
limit, DLPNO-CCSD(T1, Tight) and a composite method are the best picks among
all the localized coupled cluster methods tested for the dodecane conformers.
Dispersion-corrected dRPA-based double hybrids perform remarkably well for the
ACONFL set. While the revised reference data do not affect any conclusions on
the less accurate methods, they may upend orderings for more accurate methods
with error statistics on the same order as the difference between reference
datasets.Comment: 28 pages, submitte
Coulombic Energy Transfer and Triple Ionization in Clusters
Using neon and its dimer as a specific example, it is shown that excited
Auger decay channels that are electronically stable in the isolated monomer can
relax in a cluster by electron emission. The decay mechanism, leading to the
formation of a tricationic cluster, is based on an efficient energy-transfer
process from the excited, dicationic monomer to a neighbor. The decay is
ultrafast and expected to be relevant to numerous physical phenomena involving
core holes in clusters and other forms of spatially extended atomic and
molecular matter.Comment: 5 pages, 1 figure, to be published in PR
Investigation of the role of neutron transfer in the fusion of 32,34S with 197Au,208Pb using quasi-elastic scattering
Excitation functions for quasi-elastic scattering have been measured at
backward angles for the systems 32,34S+197Au and 32,34S+208Pb for energies
spanning the Coulomb barrier. Representative distributions, sensitive to the
low energy part of the fusion barrier distribution, have been extracted from
the data. For the fusion reactions of 32,34S with 197Au couplings related to
the nuclear structure of 197Au appear to be dominant in shaping the low energy
part of the barrier distibution. For the system 32S+208Pb the barrier
distribution is broader and extends further to lower energies, than in the case
of 34S+208Pb. This is consistent with the interpretation that the neutron
pick-up channels are energetically more favoured in the 32S induced reaction
and therefore couple more strongly to the relative motion. It may also be due
to the increased collectivity of 32S, when compared with 34S.Comment: 11 pages, 5 figure
An Exchange-Based Diagnostic for Static Correlation
We propose here a DFT-based diagnostic for static correlation %TAEX[TPSS@HF -
HF] which effectively measures how different the DFT and HF exchange energies
for a given HF density are. This and %TAEcorr[TPSS] are two cost-effective a
priori estimates for the adequacy of the importance of static correlation.
%TAEX[TPSS@HF - HF] contains nearly the same information as the earlier A
diagnostic, but may be more intuitive to understand. Principal component and
variable clustering analysis of a large number of static correlation
diagnostics reveals much of the variation is explained by just two components,
and almost all of it by four; these are blocked by four variable clusters
(single excitations; correlation entropy; double excitations; pragmatic
energetics).Comment: 5 pages, AIP Conference Proceedings, in press (ICCMSE-2021
Is explicitly correlated double hybrid DFT advantageous for vibrational frequencies?
We have investigated the effect of F12 geminals on the basis set convergence
of harmonic frequencies calculated using two representative double-hybrid
density functionals, namely B2GP-PLYP and revDSD-PBEP86-D4. Like previously
found for energetics [N. Mehta and J. M. L. Martin, \textit{J. Chem. Theor.
Comput.} \textbf{18}, 5978--5991 (2022)] one sees an acceleration by two zeta
steps, such that even the cc-pVDZ-F12 basis set is quite close to the complete
basis set (CBS) limit. However, the basis set convergence problem is not as
acute as for energetics, and compared to experimental harmonic frequencies,
conventional orbital calculations with augmented triple zeta quality basis set
are acceptably close to the CBS limit, and can be carried out using analytical
second derivatives. An efficient implementation of double hybrid-F12 analytical
derivatives would make the F12 approach attractive in the sense that even an
orbital basis set would be adequate. For the accurate revDSD-PBEP86-D4
functional, the role of differing local correlation terms (Perdew-Zunger 1981
vs. VWN5) in different electronic structure programs has been investigated:
while optimal double hybrid parameters and performance statistics for
energetics as well as frequencies differ slightly between the two
implementations, these differences are insignificant for practical purposes.Comment: Can. J. Chem., submitted (WATOC 2022 special issue
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