Toward Practical Multi-Reference Configuration Interaction Methods and Applications

Abstract

The accurate description of electronic structures in molecular systems has always been the central question in the field of quantum chemistry. For problems such as studying chemical properties of the late-row element components or investigating the energy dissipation pathways in electronically excited/ionized molecules, relativistic effects, static and dynamic electron correlations must be addressed. Despite of the simple formalism, the multireference configuration interaction (MRCI) method can treat both electron correlations and relativistic effects variationally with high accuracy. However, the large scaling of computational resources demanded by MRCI method becomes the bottleneck to apply it to any realistic systems. To shed lights on practical approaches to perform MRCI calculations, this dissertation covers important aspects including correlation space tuning to lower the number of determinants and algorithm advancements to increase the computational capability. Particularly, with the novel implementation, relativistic MRCI wavefunction with more than 1 billion determinants could be resolved using just a few computer machines. After a brief introduction to the preliminary theory concepts in Chapter 1, Chapter 2 further reviews the research and development effort for CI algorithm in the past three decades. Chapter 3 introduces a novel relativistic MRCI formalism and its distributed implementation, and parallel performance is evaluated and discussed. Chapter 4 discussed about how correlation tuning could impact MRCI calculations. Chapter 5 and 6 focused real world applications of MRCI methods to resolve X-ray absorption spectra of iron complex and study non-radiative decay pathways of electronically excited/ionized molecules, respectively.