Rimp2 Calculations

1. RI-MP2 calculations require the specification of auxiliary basis sets ($cbas) and a converged SCF calculation with the one-electron density convergence threshold set to $denconv 1.d-7 or less. In addition, the options $freeze (frozen core approximation) and $maxcor (maximum core memory usage) should be set. All these settings can be done during the input generation with the program DEFINE under the entry mp2 of last main menu.
2. Alternatively, the interactive program RIMP2PREP can be used: This program sets default values for auxiliary basis sets (data group $cbas), for frozen core orbitals (data group $freeze, all orbitals with energies below -3a.u. are suggested to be frozen) and for the amount of memory to be allocated ($maxcor. These defaults can be confirmed with return or modified, if desired. Note: the amount of memory to be allocated determines the number of multiple passes and thus the efficiency of RIMP2.
   It is also possible to run RIMP2PREP directly after DEFINE.
3. Start a single RIMP2 calculation with the command rimp2.
4. For optimisation of structure parameters at the RI-MP2 level use the command jobex -ri -level mp2.