arXiv subjects

P. Gori-Giorgi

Publications and source records attributed to P. Gori-Giorgi.

7 recordsLinked to original sources

arXiv2022

Self-Consistent Implementation of Kohn-Sham Adiabatic Connection Models with Improved Treatment of the Strong-Interaction Limit

Adiabatic connection models (ACMs), which interpolate between the limits of weak and strong interaction, are powerful tools to build accurate exchange-correlation functionals. If the exact weak-interaction expansion from second-order perturbation theory is included, a self-consistent implementation of these functionals is challenging and still absent in the literature. In this work we fill this gap by presenting a fully self-consistent-field (SCF) implementation of some popular ACM functionals. While using second-order perturbation theory at weak interactions, we have also introduced new generalised gradient approximations (GGA's), beyond the usual point-charge-plus-continuum model, for the first two leading terms at strong interactions, which are crucial to ensure robustness and reliability. We then assess the SCF-ACM functionals for molecular systems and for prototypical strong-correlation problems. We find that they perform well for both the total energy and the electronic density and that the impact of SCF orbitals is directly connected to the accuracy of the ACM functional form. For the H$_2$ dissociation the SCF-ACM functionals yield significant improvements with respect to standard functionals, also thanks to the use of the new GGA's for the strong-coupling functionals.

physics.chem-ph↗

arXiv2018

Investigation of the exchange-correlation potential of functionals based on the adiabatic connection interpolation

We have studied the correlation potentials produced by various adiabatic connection models (ACM) for several atoms and molecules. The results have been compared to accurate reference potentials (coupled cluster and quantum Monte Carlo results) as well as to state-of-the-art ab initio DFT approaches. We have found that all the ACMs yield correlation potentials that exhibit a correct behavior, quite resembling scaled second-order Görling-Levy (GL2) potentials, and including most of the physically meaningful features of the accurate reference data. The behavior and contribution of the strong-interaction limit potentials has also been investigated and discussed.

physics.chem-ph↗

arXiv2018

Restoring size consistency of approximate functionals constructed from the adiabatic connection

Approximate exchange-correlation functionals built by modeling in a non-linear way the adiabatic connection (AC) integrand of density functional theory have many attractive features, being virtually parameters-free and satisfying different exact properties, but they also have a fundamental flaw: they violate the size-consistency condition, crucial to evaluate interaction energies of molecular systems. We show that size consistency in the AC-based functionals can be restored in a very simple way at no extra computational cost. Results on a large set of benchmark molecular interaction energies show that functionals based on the interaction strength interpolation approximations are significantly more accurate than the second-order perturbation theory.

physics.chem-ph↗

arXiv2018

Assessment of interaction-strength interpolation formulas for gold and silver clusters

The performance of functionals based on the idea of interpolating between the weak and the strong-interaction limits the global adiabatic-connection integrand is carefully studied for the challenging case of noble-metal clusters. Different interpolation formulas are considered and various features of this approach are analyzed. It is found that these functionals, when used as a correlation correction to Hartree-Fock, are quite robust for the description of atomization energies, while performing less well for ionization potentials. Future directions that can be envisaged from this study and a previous one on main group chemistry are discussed.

physics.chem-ph↗

arXiv2016

The interaction-strength interpolation method for main-group chemistry: benchmarking, limitations, and perspectives

We have tested the original interaction-strength-interpolation (ISI) exchange-correlation functional for main group chemistry. The ISI functional is based on an interpolation between the weak and strong coupling limits and includes exact-exchange as well as the Görling-Levy second-order energy. We have analyzed in detail the basis-set dependence of the ISI functional, its dependence on the ground-state orbitals, and the influence of the size-consistency problem. We show and explain some of the expected limitations of the ISI functional (i.e. for atomization energies), but also unexpected results, such as the good performance for the interaction energy of dispersion-bonded complexes when the ISI correlation is used as a correction to Hartree-Fock.

physics.chem-ph↗

arXiv2015

Asymptotic behavior of the electron density and the Kohn-Sham potential in case of a Kohn-Sham HOMO nodal plane

It is known that the asymptotic decay of the electron density $n(\br)$ outside a molecule is informative about its first ionization potential $I_0$, $n(|\br|\to\infty) \sim \text{exp}(-2\sqrt{2I_0}\,r)$. This dictates the orbital energy of the highest occupied Kohn-Sham (KS) molecular orbital (HOMO) to be $ε_H=-I_0$, if the KS potential goes to zero at infinity. However, when the Kohn-Sham HOMO has a nodal plane, the KS density in that plane will decay as $\exp{(-2\sqrt{-2ε_{H-1}}\,r)}$. Conflicting proposals exist for the KS potential: from exact exchange calculations it has been found that the KS potential approaches a {\em positive} constant in the plane, but from the assumption of isotropic decay of the exact (interacting) density it has been concluded this constant needs to be {\em negative}. Here we show that either 1) the exact density decays differently (according to the second ionization potential $I_1$) in the HOMO nodal plane than elsewhere, and the KS potential has a regular asymptotic behavior (going to zero everywhere) provided that $ε_{H-1}=-I_1$; or 2) the density does decay like $\text{exp}(-2\sqrt{2I_0}\,r)$ everywhere but the KS potential exhibits strongly irregular if not divergent behavior around (at) the nodal plane.11 pages, 5 figures

physics.chem-ph↗

arXiv2011

Strictly correlated uniform electron droplets

We study the energetic properties of finite but internally homogeneous D-dimensional electron droplets in the strict-correlation limit. The indirect Coulomb interaction is found to increase as a function of the electron number, approaching the tighter forms of the Lieb-Oxford bound recently proposed by Rasanen et al. [Phys. Rev. Lett. 102, 206406 (2009)]. The bound is satisfied in three-, two-, and one-dimensional droplets, and in the latter case it is reached exactly - regardless of the type of interaction considered. Our results provide useful reference data for delocalized strongly correlated systems, and they can be used in the development and testing of exchange-correlation density functionals in the framework of density-functional theory.

cond-mat.str-el↗