arXiv subjects

Omar Madany

Publications and source records attributed to Omar Madany.

3 recordsLinked to original sources

arXiv2026

A new generation of effective core potentials: Selected heavy 5d and 6p elements

We expand the correlation-consistent effective core potentials (ccECPs) library by developing semi-local pseudopotentials and matching basis sets by heavy-elements from $5d$ (Hf, Os, Hg) and $6p$ (Tl, Po, At, Rn) blocks. In order to accurately capture scalar relativistic effects, spin-orbit coupling, and electron-electron correlation, we implement a tiered core-valence partitioning strategy across three distinct resolutions. This includes a small 60-core (Hf, Os, Hg) that explicitly correlates subvalence shells, a large 78-core definition for the main-group elements that rigorously accounts for core polarization and relaxation effects in sparse valence environments, and an intermediate 68-core partition for Hg and Tl. This 68-core architecture represents a unique development in the ccECP library, optimizing the balance between accuracy and computational efficiency in a manner unexplored for ligther elements. Optimized against relativistic all-electron CCSD(T) references, the ccECPs deliver outstanding atomic precision, achieving a global average atomic low-lying states deviation of just 0.045 eV. This accuracy translates directly to robust molecular transferability, systematically restricting dissociation energy discrepancies to under 0.03 eV, equilibrium bond lengths to within 0.005 {\AA}. By enforcing a regularized, finite potential at the origin for enhanced numerical stability in stochastic quantum Monte Carlo methods, this library removes a critical methodological bottleneck for predictive many-body simulations of heavy-element systems and materials.

physics.comp-ph↗

arXiv2025

Accurate atomic correlation and total energies for correlation consistent effective core potentials II: Rb-Xe elements

We employ correlation-consistent effective core potentials (ccECPs) to perform exact or nearly exact correlation and total energy calculations for the fifth-row elements (Rb-Xe). Total energies are calculated using various correlated methods: configuration interaction (CI), coupled-cluster (CC) up to perturbative quadruple excitations whenever feasible, and stochastic quantum Monte Carlo (QMC) approaches. In order to estimate the energy at the complete basis set (CBS) limit, the basis sets are constructed systematically through aug-cc-p(C)VnZ for each ccECP and further extrapolated to the CBS limit within the corresponding methods. Kinetic energies are evaluated at the FCI/CISD level to provide insights into the electron density and localization of the ccECPs. We also provide data sets for widely used diffusion Monte Carlo (DMC) to quantify fixed-node biases with single-reference trial wavefunctions. These comprehensive benchmarks validate the accuracy of ccECPs within the CC, CI, and QMC methodologies, thus providing accurate and tested valence-only Hamiltonians for many-body electronic structure calculations.

cond-mat.mtrl-sci↗

arXiv2025

A new generation of effective core potentials: Selected lanthanides and heavy elements II

We present a new set of correlation-consistent effective core potentials (ccECPs) for selected heavy $s$, $p$, $d$, and $f$-block elements significant in materials science and chemistry (Rb, Sr, Cs, Ba, In, Sb, Pb, Ru, Cd, La, Ce, and Eu). The ccECPs are designed using minimal Gaussian parameterization to achieve smooth and bounded potentials. They are expressed as a combination of averaged relativistic effective potentials (AREP) and effective spin-orbit (SO) terms, developed within a relativistic coupled-cluster framework. The optimization is driven by correlated all-electron (AE) atomic spectra, norm-conservation, and spin-orbit splittings, with considerations for plane wave cut-offs to ensure accuracy and viability across various electronic configurations. Transferability of these ccECPs is validated through testing on molecular oxides and hydrides, emphasizing discrepancies in molecular binding energies across a spectrum of bond lengths and electronic environments. The ccECPs demonstrate excellent agreement with AE reference calculations, attaining chemical accuracy in bond dissociation energies and equilibrium bond lengths, even in systems characterized by substantial relativistic and correlation effects. These ccECPs provide accurate and transferable framework for valence-only calculations.

cond-mat.mtrl-sci↗