Handling Time and Temperature in Materials Simulations

Abstract

Presented is an approach based on the seamless transmission of information obtained from modern electronic structure methods like density‐functional theory to thermodynamic functions. It allows to circumvent short term dynamics in a system, instead focusing on the long‐term impact an environment can have on it. It allows the identification of stable and metastable phases at relevant ( T,p )‐conditions. After outlining the basic principles of the methodology, examples of surfaces in contact with realistic environments are used to emphasise or illustrate different aspects of the method. Particular attention is paid to possible approximations and their justification is discussed. The use of a direct screening approach, in which relevant structures are directly compared, as a possibility to deal with the configurational diversity of a system is discussed. Its advantages and disadvantages are discussed, and alternative routes are suggested. The importance of surface vibrational entropy is discussed in some depth, since it can have a large impact on formation Gibbs free energies and thus on the competition between relevant structures to gain thermodynamic stability at a given temperature. The assumption underlying the thermodynamic approach are reviewed and routes to extend the thermodynamic formalism to account for kinetically stabilised surface reconstructions are presented. Experimental situations, which may give rise to chemical potentials beyond the thermodynamic limit are mentioned. Examples of equilibrium, extended and meta‐stable surface phase diagrams are shown and discussed.