Laplace transform techniques in Mo/ller–Plesset perturbation theory

We discuss how the computational obstacles related to energy denominators in various schemes for electron-correlation calculations can be circumvented by a Laplace transform technique. The method is applicable to a wide variety of electronic structure calculations. We discuss in detail an algorithm for the contribution of triple excitations in fourth-order Mo/ller–Plesset perturbation theory, which grows only with the sixth power of the size of the system, as compared to conventional N7 algorithms. Special consideration is given to efficient schemes for numerical quadrature of the integrals occurring in the Laplace transformations.