Range separated hybrids of pair coupled cluster doubles and density functionals

2015 ◽  
Vol 17 (34) ◽  
pp. 22412-22422 ◽  
Author(s):  
Alejandro J. Garza ◽  
Ireneusz W. Bulik ◽  
Thomas M. Henderson ◽  
Gustavo E. Scuseria
Keyword(s):  
Low Cost ◽  
Coupled Cluster ◽  
Density Functionals ◽  
Dynamic Correlation

Using the technique of range separation, we combine pair coupled cluster doubles (pCCD) with density functionals in order to incorporate dynamic correlation in pCCD while maintaining its low cost.

scholarly journals Double Excitations from Ensemble Density Functionals: Theory and Approximations

2021 ◽  
Author(s):  
Tim Gould ◽  
Leeor Kronik ◽  
Stefano Pittalis
Keyword(s):  
Density Functional ◽  
Low Cost ◽  
Slater Determinant ◽  
Density Functionals ◽  
Functional Theory ◽  
Fluctuation Dissipation ◽  
Highest Occupied Molecular Orbital ◽  
Pair Density ◽  
Structure Calculations ◽  
Shed Light

Double excitations, which are dominated by a Slater-determinant with both electrons in the highest occupied molecular orbital promoted to the lowest unoccupied orbital(s), pose significant challenges for low-cost electronic structure calculations based on density functional theory (DFT). Here, we demonstrate that recent advances in ensemble DFT [<i>Phys. Rev. Lett.</i> <b>125</b>, 233001 (2020)], which extend concepts of ground-state DFT to excited states via a rigorous physical framework based on the ensemble fluctuation-dissipation theorem, can be used to shed light on the double excitation problem. We find that the exchange physics of double excitations is reproducible by standard DFT approximations using a linear combination formula, but correlations are more complex. We then show, using selected test systems, that standard DFT approximations may be adapted to tackle double excitations based on theoretically motivated simple formulae that employ ensemble extensions of expressions that use the on-top pair density.<br><br>

scholarly journals Actinide chemistry using singlet-paired coupled cluster and its combinations with density functionals

2015 ◽  
Vol 143 (24) ◽  
pp. 244106 ◽  
Author(s):  
Alejandro J. Garza ◽  
Ana G. Sousa Alencar ◽  
Gustavo E. Scuseria
Keyword(s):  
Coupled Cluster ◽  
Density Functionals ◽  
Actinide Chemistry

scholarly journals Density Functionals with Quantum Chemical Accuracy: From Machine Learning to Molecular Dynamics

2019 ◽  
Author(s):  
Mihail Bogojeski ◽  
Leslie Vogt-Maranto ◽  
Mark E. Tuckerman ◽  
Klaus-Robert Mueller ◽  
Kieron Burke
Keyword(s):  
Machine Learning ◽  
Molecular Dynamics ◽  
Quantum Chemical ◽  
Density Functional ◽  
Md Simulations ◽  
Training Data ◽  
Coupled Cluster ◽  
Density Functionals ◽  
Cluster Accuracy ◽  
Single Water Molecule

<div> <div> <div> <p>Kohn-Sham density functional theory (DFT) is a standard tool in most branches of chemistry, but accuracies for many molecules are limited to 2-3 kcal/mol with presently-available functionals. <i>Ab initio </i>methods, such as coupled-cluster, routinely produce much higher accuracy, but computational costs limit their application to small molecules. We create density functionals from coupled-cluster energies, based only on DFT densities, via machine learning. These functionals attain quantum chemical accuracy (errors below 1 kcal/mol). Moreover, density-based ∆-learning (learning only the correction to a standard DFT calculation, ∆-DFT) significantly reduces the amount of training data required. We demonstrate these concepts for a single water molecule, and then illustrate how to include molecular symmetries with ethanol. Finally, we highlight the robustness of ∆-DFT by correcting DFT simulations of resorcinol on the fly to obtain molecular dynamics (MD) trajectories with coupled-cluster accuracy. Thus ∆-DFT opens the door to running gas-phase MD simulations with quantum chemical accuracy, even for strained geometries and conformer changes where standard DFT is quantitatively incorrect. </p> </div> </div> </div>

Accurate dipole polarizabilities for water clusters n=2–12 at the coupled-cluster level of theory and benchmarking of various density functionals

2009 ◽  
Vol 131 (21) ◽  
pp. 214103 ◽  
Author(s):  
Jeff R. Hammond ◽  
Niranjan Govind ◽  
Karol Kowalski ◽  
Jochen Autschbach ◽  
Sotiris S. Xantheas
Keyword(s):  
Water Clusters ◽  
Coupled Cluster ◽  
Density Functionals ◽  
Cluster Level ◽  
Dipole Polarizabilities

scholarly journals Capturing Static and Dynamic Correlation with ΔNO-MP2 and ΔNO-CCSD

2019 ◽  
Author(s):  
joshua wallace hollett ◽  
Pierre-Francois Loos
Keyword(s):  
Perturbation Theory ◽  
Potential Energy ◽  
Second Order ◽  
Potential Energy Curves ◽  
Coupled Cluster ◽  
Dynamic Correlation ◽  
Static Correlation ◽  
Selection Of ◽  
Plesset Perturbation Theory ◽  
Good Agreement

<p>The NO method for static correlation is combined with second-order Mller-Plesset perturbation theory (MP2) and coupled-cluster singles and doubles (CCSD) to account for dynamic correlation. The MP2 and CCSD expressions are adapted from nite-temperature CCSD, which includes orbital occupancies and vacancies, and expanded orbital summations. Correlation is partitioned with the aid of damping factors incorporated into the MP2 and CCSD residual equations. Potential energy curves for a selection of diatomics are in good agreement with extrapolated full conguration interaction results (exFCI), and on par with conventional multireference approaches.<br></p>

Post-Hartree-Fock Methods and Electron Correlation: A Very Brief Overview

2020 ◽  
pp. 379-399
Author(s):  
Jochen Autschbach
Keyword(s):  
Electron Correlation ◽  
Electron System ◽  
Open Shell ◽  
Basis Set ◽  
Coupled Cluster ◽  
Hartree Fock ◽  
Dynamic Correlation ◽  
Static Correlation ◽  
Full Ci ◽  
Virtual Orbitals

‘This chapter sketches how the electron correlation is treated in post-Hartree-Fock (HF) wavefunction methods. The distinction between static and dynamic correlation is explained. A configuration interaction (CI) wavefunction is a linear combination of several or many Slater determinants (SDs). Following a HF calculation, different SDs can be constructed by replacing 1, 2, 3, … occupied orbitals in the HF wavefunction with 1, 2, 3,… unoccupied or virtual orbitals, leading to pseudo-excited electron configurations at the singles, doubles, triples, … (S, D, T, …) level. The virtual orbitals are usually available as a by-product of the HF calculation in a basis set. Full CI (FCI) considers all possible substitutions, up to N-fold for an N-electron system. FCI is impractical for all but the smallest molecules. CI truncated at a lower level, e.g. S and D, suffers from lack of size extensitivity. Truncated coupled-cluster (CC) is size extensive. Open-shell systems generally require a multi-reference treatment. The chapter concludes with a treatment of the static correlation in the bond breaking of H2.

scholarly journals Capturing Static and Dynamic Correlation with ΔNO-MP2 and ΔNO-CCSD

2019 ◽  
Author(s):  
joshua wallace hollett ◽  
Pierre-Francois Loos
Keyword(s):  
Perturbation Theory ◽  
Potential Energy ◽  
Second Order ◽  
Potential Energy Curves ◽  
Coupled Cluster ◽  
Dynamic Correlation ◽  
Static Correlation ◽  
Selection Of ◽  
Plesset Perturbation Theory ◽  
Good Agreement

<p>The NO method for static correlation is combined with second-order Mller-Plesset perturbation theory (MP2) and coupled-cluster singles and doubles (CCSD) to account for dynamic correlation. The MP2 and CCSD expressions are adapted from nite-temperature CCSD, which includes orbital occupancies and vacancies, and expanded orbital summations. Correlation is partitioned with the aid of damping factors incorporated into the MP2 and CCSD residual equations. Potential energy curves for a selection of diatomics are in good agreement with extrapolated full conguration interaction results (exFCI), and on par with conventional multireference approaches.<br></p>

Sign in / Sign up

Export Citation Format

Share Document