A Reduced Cost Two-component Relativistic Equation-of-Motion Coupled Cluster Method for Ionization Potential

TL;DR

This paper introduces an efficient relativistic IP-EOM-CC method using X2CAMF, CD, and FNS techniques, enabling accurate ionization potential calculations for heavy-element molecules with reduced computational cost.

Contribution

The paper presents a novel, computationally efficient implementation of the relativistic IP-EOM-CC method for heavy molecules, combining X2CAMF, Cholesky decomposition, and frozen natural spinors.

Findings

Method achieves results nearly identical to four-component calculations.

Good agreement with experimental ionization energies and spectra.

Successfully applied to a medium-sized heavy-element complex.

Abstract

We report an efficient implementation of the ionization potential (IP) variant of the equation-of-motion coupled cluster (IP-EOM-CC) method based on the exact two-component atomic mean field (X2CAMF) framework, utilizing Cholesky decomposition (CD) and frozen natural spinors (FNS). The CD approximation significantly reduces memory demands, whereas the FNS approximation lowers the number of floating-point operations. Together, these techniques make the method computationally efficient for accurate relativistic IP-EOM-CC calculations of molecules containing heavy elements. The calculated IP values are almost identical to those obtained by the four-component relativistic IP-EOM-CC method. Benchmark studies show good agreement with experimental ionization energies and photoelectron spectra, demonstrating the method's reliability. The practical applicability of the approach is demonstrated by IP calculations on the medium-sized [I(H$_{2}$O)$_{12}$]$^{-}$ complex, with 1698 virtual spinors.