A lower scaling four-component relativistic coupled cluster method based on natural spinors

TL;DR

This paper introduces a new relativistic coupled cluster method using frozen natural spinors that improves convergence and reduces errors, making high-accuracy calculations more efficient and user-friendly.

Contribution

The paper develops a lower scaling four-component relativistic coupled cluster method based on natural spinors, enhancing convergence and accuracy control over previous approaches.

Findings

Faster convergence of correlation energy with natural spinors

Perturbative correction smooths property convergence

Significant reduction in truncation errors

Abstract

We present the theory, implementation, and benchmark results for a frozen natural spinors-based lower scaling four-component relativistic coupled cluster method. The natural spinors are obtained by diagonalizing the one-body reduced density matrix from a relativistic MP2 calculation based on four-component Dirac-Coulomb Hamiltonian. The correlation energy in the coupled cluster method converges more rapidly with respect to the size of the virtual space in the frozen natural spinor basis than that observed in the standard canonical spinors obtained from the Dirac-Hartree-Fock calculation. The convergence of properties is not smooth in the frozen natural spinor basis. However, the inclusion of the perturbative correction smoothens the convergence of the properties with respect to the size of the virtual space in the frozen natural spinor basis and greatly reduces the truncation errors for both energy and properties calculations. The accuracy of the frozen natural spinor based coupled cluster methods can be controlled by a single threshold and is a black box to use.