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Thursday, February 28

Linear Scaling Electronic Structure Calculations Using Coupled Cluster Wave Function Models

Professor Poul Joergensen, Aarhus University, Langelandsgade, Denmark
Joint Institute for Computational Sciences Seminar
1:00 PM — 2:00 PM, Joint Institute for Computational Sciences (JICS) Lecture Hall, Building 5100, Room 262
Contact: Donna Wilkerson (djx@ornl.gov), 865.574.5493

Abstract

Standard implementations of coupled cluster wave function models are expressed in a set of canonical Hartree-Fock orbitals and exhibit a scaling wall which prevents coupled cluster calculations from being carried out for any but the smallest molecular systems. The major task of a coupled cluster calculation is to describe the short-range (local) electron correlation effects (Coulomb holes and dispersion forces). Expressing local phenomena in the non-local canonical Hartree-Fock basis inherently leads to the scaling wall. However, by expressing the coupled cluster calculations in a local Hartree-Fock basis the calculations can be completely restructured and carried out in terms of calculations on small orbital fragments. This leads to a linear scaling algorithm.

We show how the above strategy can be implemented for the second order Møller-Plesset (MP2), the coupled cluster singles and doubles (CCSD), and the CCSD with perturbative triples [CCSD(T)] models. The latter is the golden standard of electronic structure calculations. Calculations are presented for the MP2 model for molecular systems containing about 1000 atoms and 10000 basis functions. The calculations show perfect scalability with respect to system size and with respect to the number of nodes for up to 6000 nodes on Titan.