CERES: An ab initio code dedicated to the calculation of the electronic structure and magnetic properties of lanthanide complexes

TL;DR

CERES is a new C++11 ab initio code that efficiently calculates electronic structures and magnetic properties of lanthanide complexes, improving speed and accuracy over existing methods.

Contribution

The paper introduces CERES, a novel ab initio code with optimized algorithms for lanthanide systems, enabling faster and more comprehensive magnetic property calculations.

Findings

CERES outperforms current methods in computational efficiency.

The code accurately models non-perturbative spin-orbit effects.

CERES provides reliable predictions of crystal field levels.

Abstract

We have developed and implemented a new ab initio code, CERES (Computational Emulator of Rare Earth Systems), completely written in C++11, which is dedicated to the efficient calculation of the electronic structure and magnetic properties of the crystal field states arising from the splitting of the ground state spin-orbit multiplet in lanthanide complexes. The new code gains efficiency via an optimised implementation of a direct configurational averaged Hartree-Fock (CAHF) algorithm for the determination of $4f$ quasi-atomic active orbitals common to all multi-electron spin manifolds contributing to the ground spin-orbit multiplet of the lanthanide ion. The new CAHF implementation is based on quasi-Newton convergence acceleration techniques coupled to an efficient library for the direct evaluation of molecular integrals, and problem-specific density matrix guess strategies. After describing the main features of the new code, we compare its efficiency with the current state--of--the--art ab initio strategy to determine crystal field levels and properties, and show that our methodology, as implemented in CERES, represents a more time-efficient computational strategy for the evaluation of the magnetic properties of lanthanide complexes, also allowing a full representation of non-perturbative spin-orbit coupling effects.