A generalized variational principle with applications to excited state mean field theory
Abstract
We present a generalization of the variational principle that is compatible with any Hamiltonian eigenstate that can be specified uniquely by a list of properties. This variational principle appears to be compatible with a wide range of electronic structure methods, including meanfield theory, density functional theory, multireference theory, and quantum Monte Carlo. Like the standard variational principle, this generalized variational principle amounts to the optimization of a nonlinear function that, in the limit of an arbitrarily flexible wave function, has the desired Hamiltonian eigenstate as its global minimum. Unlike the standard variational principle, it can target excited states and select individual states in cases of degeneracy or neardegeneracy. As an initial demonstration of how this approach can be useful in practice, we employ it to improve the optimization efficiency of excited state mean field theory by an order of magnitude. With this improved optimization, we are able to demonstrate that the accuracy of the corresponding secondorder perturbation theory rivals that of singlesanddoubles equationofmotion coupled cluster in a substantially broader set of molecules than could be explored by our previous optimization methodology.
 Publication:

arXiv eprints
 Pub Date:
 October 2019
 arXiv:
 arXiv:1910.03145
 Bibcode:
 2019arXiv191003145S
 Keywords:

 Physics  Chemical Physics;
 Condensed Matter  Strongly Correlated Electrons