6.6 Auxiliary Basis (Resolution of the Identity) MP2 Methods

6.6.2 OpenMP Implementation of RI-MP2

An OpenMP RI-MP2 energy algorithm is used by default in Q-Chem 4.1 onward. This can be invoked by using CORR=primp2 for older versions, but note that in 4.01 and below, only RHF/RI-MP2 was supported. Now UHF/RI-MP2 and ROHF/RI-MP2 is supported, and the formation of the ‘B’ matrices as well as three center integrals are parallelized. This algorithm uses the remaining memory from the MEM_TOTAL allocation for all computation, which can drastically reduce hard drive reads in the formation of t-amplitudes. Since Q-Chem 5.2, RI-MP2 can be invoked by using method=mp2 and proper auxiliary basis using AUX_BASIS_CORR. In case of double-hybrid, adding AUX_BASIS_CORR will simply invoke RI-MP2.

Example 6.4  Example of OpenMP-parallel RI-MP2 job.

   0 1
   H1  C1    1.077260
   H2  C1    1.077260  H1  131.608240

   EXCHANGE           HF
   BASIS              cc-pVTZ
   AUX_BASIS          rimp2-cc-pVTZ
   PURECART           11111
   SYMMETRY           false
   THRESH             12
   !TIME_MP2          true