Geometry optimizations with spinor-based relativistic coupled-cluster theory

Abstract

Development of analytic gradients for relativistic coupled-cluster singles and doubles augmented with a non-iterative triples [CCSD(T)] method using an all-electron exact two-component Hamiltonian with atomic mean-field spin-orbit integrals (X2CAMF) is reported. This enables efficient CC geometry optimizations with spin-orbit coupling included in orbitals. The applicability of the implementation is demonstrated using benchmark X2CAMF-CCSD(T) calculations of equilibrium structures and harmonic vibrational frequencies for methyl halides, CH3X, X=Br, I, At, as well as calculations of rotational constants and infrared spectrum for RaSH+, a radioactive molecular ion of interest to spectroscopic study.

Route to Chemical Accuracy for Computational Uranium Thermochemistry

“…The calculations of electronic energies for UO, UO + , UO 2 + , and UO 2 have been carried out using the structures optimized at the X2CAMF-CCSD­(T)/VTZ level, as summarized in Table . The calculations of equilibrium structures for UO, UO + , UO 2 + , and UO 2 have been performed using the recent implementation of analytic X2CAMF-CCSD­(T) gradients . The calculations of harmonic frequencies have been expedited by means of numerical differentiation of analytic gradients …”

“…The calculations of equilibrium structures for UO, UO + , UO 2 + , and UO 2 have been performed using the recent implementation of analytic X2CAMF-CCSD(T) gradients. 90 The calculations of harmonic frequencies have been expedited by means of numerical differentiation of analytic gradients. 91 Unless otherwise stated, the X2CAMF calculations have used the valence occupation numbers of the electronic ground states of the neutral atoms, that is, U(5f 3 6d 1 7s 2 ) and O(2s 2 2p 6 ), for the calculations of the spherical atoms in the construction of the X2CAMF integrals.…”

Relativistic coupled-cluster calculations of RaOH pertinent to spectroscopic detection and laser cooling

“…The calculations of equilibrium structures for RaOH have been facilitated by the recent development of analytic X2CAMF-CCSD(T) and EOM-CCSD gradients. 75 The harmonic vibrational frequencies of RaOH have been evaluated by means of numerical differentiation of analytically evaluated gradients. 76…”

“…The calculations of equilibrium structures for RaOH have been facilitated by the recent development of analytic X2CAMF-CCSD(T) and EOM-CCSD gradients. 75 The harmonic vibrational frequencies of RaOH have been evaluated by means of numerical differentiation of analytically evaluated gradients. 76 Paper PCCP The electronic energies for the X 2 S, A 2 P 1/2 , B 2 D 3/2 , and C 2 S states of RaF and RaOH have been calculated at the HF, CCSD, and CCSD(T) levels with systematically enlarged basis sets using the X2CAMF-CCSD(T) equilibrium structures.…”

Cholesky Decomposition-Based Implementation of Relativistic Two-Component Coupled-Cluster Methods for Medium-Sized Molecules

“…Molecules containing heavy elements play increasingly important roles in a variety of research areas, ranging from catalysis, – medicine, – optoelectronic devices, – to quantum simulation, – and the search of new physics beyond the Standard Model. – Accurate treatments of both relativistic effects – and electron correlation – are required for reliable predictions of molecular properties for heavy-element-containing molecules. Combining coupled-cluster (CC) , and equation-of-motion CC (EOM-CC) methods , with relativistic four- and two-component Hamiltonians, the spinor-based relativistic CC and EOM-CC methods – and analytic derivative techniques – have emerged as useful tools for chemical applications involving heavy-element-containing molecules aiming at high accuracy. Among the relativistic CC methodologies, the four-component CC methods based on the Dirac–Coulomb­(–Breit) Hamiltonian , are the most rigorous but computationally the most expensive.…”