Calculation of the static and dynamical correlation energy of pseudo-one-dimensional beryllium systems via a many-body expansion

TL;DR

This paper applies a multireference method of increments to study static and dynamical correlation energies in low-dimensional beryllium systems, successfully describing their dissociation curves from small clusters to infinite chains.

Contribution

It introduces a multireference approach using the method of increments for extended Be systems, providing insights into their correlation energies across dissociation.

Findings

Successful application of CAS-MoI to Be6 ring

Extension of the method to larger rings and infinite chains

Analysis of basis set effects on correlation energy calculations

Abstract

Low-dimensional beryllium systems constitute interesting case studies for the test of correlation methods because of the importance of both static and dynamical correlation in the formation of the bond. Aiming to describe the whole dissociation curve of extended Be systems we chose to apply the method of increments (MoI) in its multireference (MR) formalism. However, in order to do so an insight into the wave function was necessary. Therefore we started by focusing on the description of small Be chains via standard quantum chemical methods and gave a brief analysis of the main characteristics of their wave functions. We then applied the MoI to larger beryllium systems, starting from the Be6 ring. First, the complete active space formalism (CAS-MoI) was employed and the results were used as reference for local MR calculations of the whole dissociation curve. Despite this approach is well established for the calculation of systems with limited multireference character, its application to the description of whole dissociation curves still requires further testing. After discussing the role of the basis set, the method was finally applied to larger rings and extrapolated to an infinite chain.