Keywords Valid for Both MPGRAD and RIMP2

$maxcor n

The data group $maxcor adjusts the maximum size of core memory (n in MB) which will be allocated during the MP2 run. Recommendation: 3/4 of the actual main memory at most. If $maxcor is not found, its value is set to 200 MB.

$mp2energy

Calculation of MP2 gradient is omitted, only MP2 energy is calculated. In connection with this keyword you may also activate the spin-component-scaled (SCS) MP2 proposed by Grimme

$mp2energy SCS

with the default values of 6/5 for pS and 1/3 for pT, which may be modified this way:

$mp2energy SCS pt=val1 ps=val2

$freeze
 a1g     1-2
 t1u     1

The data group $freeze specifies frozen orbitals, in the above syntax by irreducible representations. The symmetry-independent and for standard-applications recommended syntax is

$freeze
 implicit core=5 virt=2

This will freeze the 5 lowest occupied and 2 highest virtual orbitals (alpha and beta count as one in UHF cases). Note that degenerate orbitals count twice (e representations), thrice (t representations) etc. In case of mpgrad frozen orbitals have to be specified manually, for rimp2 the preparation tool rimp2prep may be used to specify frozen core orbitals, frozen virtuals have to be specified manually. Note: In case of gradient calculations frozen core orbitals are regarded only by rimp2, but not by mpgrad, moreover freezing of virtual orbitals is generally not supported by mpgrad.