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

• Published in: Journal of computational chemistry Vol. 39; no. 6; pp. 328 - 337
• Main Authors: Calvello, Simone, Piccardo, Matteo, Rao, Shashank Vittal, Soncini, Alessandro
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 05.03.2018
• Subjects: ab initio; Atomic structure; configurational average; Coupling (molecular); crystal field levels; Crystal structure; Electron spin; Electronic structure; electronic structure theory; Evaluation; lanthanide single molecule magnets; Magnetic properties; Mathematical analysis; Quantum theory; Rare earth elements; Spin-orbit interactions; ab initio; electronic structure theory; lanthanide single molecule magnets; configurational average; crystal field levels
• ISSN: 0192-8651; 1096-987X
• DOI: 10.1002/jcc.25113

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 optimized 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. © 2017 Wiley Periodicals, Inc. Lanthanide single molecule magnets are important systems for the development of molecular memories, with ab initio methodologies being an important tool for their characterization. In this work, we present a new software for the calculation of crystal field states for lanthanide single molecule magnets. Based on a new method we recently developed, we compare it with a currently available program, showing that our method is more efficient without any significant loss in accuracy.