Oxygen Defect Formation Thermodynamics of CaMnO3: A Closer Look

Abstract

Sustainable hydrogen production is one of the most important topics in modern energy economics. Of technological relevance are, for example, electrochemical and thermal splitting of water. For such processes anode materials with a variable concentration of oxygen defects are required. Herein, the oxygen defect thermochemistry of a possible anode material, the perovskite CaMnO3, is investigated theoretically. The aim of this work is to identify reliable quantum chemical methods for the calculation of oxygen defect formation enthalpies and entropies, including configuration entropy, which is usually neglected. All possible defect configurations in a supercell are computed to obtain the configuration entropy using Boltzmann statistics. Various generalized gradient approximation (GGA), meta‐GGA, and hybrid functionals as implemented in the solid‐state programs CRYSTAL and VASP are evaluated for the calculation of structure parameters, electronic and magnetic properties, and reaction energies of CaMnO3. The global hybrid functional PW1PW gives the most accurate overall description of CaMnO3 and is therefore recommended for future theoretical studies of more efficient water‐splitting catalysts based on calcium manganate.