Materials Simulation From First-Principles: Fundamental Challenges and Importance of Finite Temperature Modeling

The discovery of the extraordinary activity in catalysis exhibited by small clusters has stimulated considerable research interest. However, in heterogeneous catalysis, materials property changes under operational environment (i.e. at a finite temperature (T) and pressure (p) in an atmosphere of reactive molecules). Therefore, a solid theoretical understanding at a realistic (T, p) is essential in order to address the underlying phenomena.
       This talk is, therefore, driven by the vision of computational design of materials at a finite (T, p). Here, I shall introduce a robust methodological approach that integrates various levels of theories combined into one multi-scale simulation to address the environmental effect to predict the  properties of materials at a finite T, p. Our approach employs density-functional theory (DFT) combined with ab initio atomistic thermodynamics^[1]. In order to quantitatively account the contribution of anharmonic vibrational free energy to the configurational entropy, we have evaluated the excess free energy of selected clusters numerically by thermodynamic integration method with DFT inputs. We further establish the necessity of this finite temperature modeling as DFT (with appropriate exchange and correlation functionals) fails to predict the stable phases even at a moderately low temperature. We have successfully applied our finite temperature modeling approach in various inter-disciplinary fields viz. (i) catalysis^[2-3], (ii) defects in semi-conductor^[4], (iii) energy materials[5-6], etc. I shall discuss in details one application^[6] of this methodology in addressing (T, p) dependence on the composition, structure, thermodynamic stability of metal hydride clusters in a reactive atmosphere in the context of designing energy materials.