Prerequisites

Calculations with MPGRAD or RIMP2 require

• a converged SCF calculation with the one-electron density convergence threshold set to $denconv 1.d-7 or less
• the maximum core memory the program is allowed to allocate should be defined in the data group $maxcor (in MB); the recommended value is ca. 3/4 of the available (physical) core memory at most.
• orbitals to be excluded from the correlation treatment have to be specified in data group $freeze
• the calculation of MP2 gradients is omitted by adding the flag $mp2energy to the control file; in this case only MP2 energy is calculated.

Calculations with RIMP2 moreover require

• an auxiliary basis defined in the data group $cbas

this is not needed for MPGRAD , but here one needs

• a specification for scratch files and their size in data group $mointunit (see Section 14.2.12)
• and the number of passes for integral evaluations and transformations in data group $traloop