Theoretical chemistry is concerned with understanding, describing and predicting chemistry using theories. The basic theoretical principles derive from fundamental physical laws expressed by mathematical equations. Although too complicated to be exactly solvable, approximate, accurate and useful theories can be developed that can be implemented in computer programs. Thereby theory can be used to interpret, predict, confirm or reject experimental results using brains and computers.
With an initial focus on describing the electronic structure of molecules, I have over time sought a more complete picture emphasizing also environmental effects and (quantum) molecular dynamics. All these aspects are typically important for describing reality, but the level of maturity of theories for actual computations is quite different, in particular with respect to the size of the system that can be realistically treated.
A major focus point of our current research is the development of fundamentally new computational methods for the quantum description of molecular dynamics. In the long perspective our aim is to develop methods applicable to molecular systems containing 10-1000s of atoms. Such systems are presently completely out of reach of accurate quantum computations.
An essential ingredient of the present work is the use of coupled cluster theory for the description of the dynamics of the atomic nuclei. Coupled cluster (CC) theory has long been accepted as providing the golden standard for electronic structure where we have developed and applied it in many different contexts. We have defined the vibrational coupled cluster (VCC) approach and developed detailed theory and computational implementations for it.