Analysis of and remedies for unphysical ground states of the multireference averaged coupled-pair functional.
A Multireference Configuration Interaction (MRCI) wavefunction includes both static and dynamic electron correlation. MRCI's well-known flaw, a lack of size extensivity, can be ameliorated with the Multireference Averaged Coupled-Pair Functional (MRACPF). However, the original MRACPF is frequently unstable, sometimes producing unphysical results. The more Multireference Averaged Quadratic Coupled-Cluster and MRACPF2 functionals also occasionally exhibit unphysical behavior. We find that these instabilities are avoided crossings with unphysical solutions to the MRACPF equations. We present two approaches to avoid the undesirable unphysical solutions.
Department of Chemistry, Princeton University, Princeton, New Jersey 08544-1009, USA.
David B
DB
Krisiloff
Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544-5263, USA.
Victor B
VB
Oyeyemi
Institute for Theoretical Physics, Vienna University of Technology, Vienna, Austria.
Florian
F
Libisch
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544-5263, USA; Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544, USA; and Andlinger Center for Energy and the Environment, Princeton University, Princeton, New Jersey 08544-5263, USA.
Emily A
EA
Carter