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

A Cholesky decomposition (CD)-based implementation of
relativistic
two-component coupled-cluster (CC) and equation-of-motion CC (EOM-CC)
methods using an exact two-component Hamiltonian augmented with atomic-mean-field
spin–orbit integrals (the X2CAMF scheme) is reported. The present
CD-based implementation of X2CAMF-CC and EOM-CC methods employs atomic-orbital-based
algorithms to avoid the construction of two-electron integrals and
intermediates involving three and four virtual indices. Our CD-based
implementation extends the applicability of X2CAMF-CC and EOM-CC methods
to medium-sized molecules with the possibility to correlate around
1000 spinors. Benchmark calculations for uranium-containing small
molecules were performed to assess the dependence of the CC results
on the Cholesky threshold. A Cholesky threshold of 10–4 is shown to be sufficient to maintain chemical accuracy. Example
calculations to illustrate the capability of the CD-based relativistic
CC methods are reported for the bond-dissociation energy of the uranium
hexafluoride molecule, UF6, with up to quadruple-ζ
basis sets, and the lowest excitation energy in the solvated uranyl
ion [UO22+(H2O)12].