An Efficient Parallel Algorithm for the Calculation of Unrestricted Canonical MP2 Energies

We present details of our efficient implementation of full accuracy unrestricted open-shell second-order canonical Moller-Plesset (MP2) energies, both serial and parallel. The algorithm is based on our previous restricted closed-shell MP2 code using the Saebo-Almlof direct integral transformation. Depending on system details, UMP2 energies take from less than 1.5 to about 3.0 times as long as a closed-shell RMP2 energy on a similar system using the same algorithm. Several examples are given including timings for some large stable radicals with 90- atoms and over 3600 basis functions. (C) 2011 Wiley Periodicals, Inc. J Comput Chem 32: 3304-3312, 2011