Role of exact exchange in thermally-assisted-occupation density functional theory: A proposal of new hybrid schemes

Abstract

We propose hybrid schemes incorporating exact exchange into thermally-assisted-occupation density functional theory (TAO-DFT) [J.-D. Chai, J. Chem. Phys. 136, 154104 (2012)] for an improved description of nonlocal exchange effects. With a few simple modifications, global and range-separated hybrid functionals in Kohn-Sham density functional theory (KS-DFT) can be combined seamlessly with TAO-DFT. In comparison with global hybrid functionals in KS-DFT, the resulting global hybrid functionals in TAO-DFT yield promising performance for systems with strong static correlation effects (e.g., the dissociation of H 2 and N 2 , twisted ethylene, and electronic properties of linear acenes), while maintaining similar performance for systems without strong static correlation effects. Besides, a reasonably accurate description of noncovalent interactions can be efficiently achieved through the inclusion of dispersion corrections in hybrid TAO-DFT. Relative to semilocal density functionals in TAO-DFT, global hybrid functionals in TAO-DFT are generally superior in performance for a wide range of applications, such as thermochemistry, kinetics, reaction energies, and optimized geometries.

Fate of the open-shell singlet ground state in the experimentally accessible acenes: A quantum Monte Carlo study

“…For the particle-particle RPA (ppRPA) calculations 14 , the plotted quantity is the weight of the MO dominant configuration in the RPA expansion. For the thermally-assistedoccupation B3LYP (TAO-B3LYP) approach 35 , the reported thermally populated occupations should tend to the natural orbitals ones by virtue of the chosen effective temperature. For our QMC calculations, we compute the occupations of the NO representation of the determinantal part, which strictly speaking are not the natural occupations of the full wave function.…”

Effect of Li Termination on the Electronic and Hydrogen Storage Properties of Linear Carbon Chains: A TAO-DFT Study

“…for the lowest singlet state of C n /Li 2 C n as a function of the chain length, using TAO-BLYP-D. Here, f i the occupation number of the i th orbital obtained with TAO-BLYP-D, which varies from 0 to 1, is approximately equal to the occupation number of the i th natural orbital [46][47][48]58]. For a system without strong static correlation ({f i } are close to either 0 or 1), S vN provides insignificant contributions, while for a system with strong static correlation ({f i } are fractional for active orbitals, and are close to either 0 or 1 for others), S vN increases with the number of active orbitals.…”

“…To circumvent the formidable computational expense of high-level ab initio multireference methods, we have newly developed thermally-assisted-occupation density functional theory (TAO-DFT) [46][47][48] for the study of large ground-state systems (e.g., containing up to a few thousand electrons) with strong static correlation effects. In contrast to KS-DFT, TAO-DFT is a density functional theory with fractional orbital occupations, wherein strong static correlation is explicitly described by the entropy contribution (see Eq.…”

Electronic and Hydrogen Storage Properties of Li-Terminated Linear Boron Chains Studied by TAO-DFT

“…For the exact theory, the lowest singlet energies of Li 2 B n obtained with spin-restricted and spin-unrestricted calculations should be identical, due to the symmetry constraint 46 – 48 , 60 . To see if this property remains valid here, spin-restricted TAO-BLYP-D calculations are additionally performed for the lowest singlet energies on the corresponding optimized geometries.…”

“…Here, we assess the multi-reference character of Li 2 B n by calculating the symmetrized von Neumann entropy 47 , 48 , 53 , 55 – 57 , 60 for the ground state of Li 2 B n . In Eq.…”