13.2 Restarting calculations

By default, and in all examples shown so far, scratch files are used to store all intermediate data MOLPRO needs, and the user will normally not see these files at all. However, it is possible to save computed data as orbitals and energies in named (permanent) files and use these for restarting a calculation at a later stage. MOLPRO uses a number of different files, but only one or two of them are needed for a restart. File 1 holds the one- and two electron integrals and related information, while on file 2 the wavefunction information like orbitals, orbital energies, and optionally CI-vectors are stored. Thus, file 2 is essential for restarting a calculation, while the integrals on file 1 can either be restarted or recomputed.

The use of named files can be requested using the file directive, which should be given immediately after the memory command (if present), e.g.,

***,title
memory,16,m            !allocate 16 MW of memory
file,1,filename.int    !allocate permanent integral file
file,2,filename.wfu    !allocate permanent wave-function (dump) file
geometry={...}         !define the nuclear coordinates
basis=vdz              !Select basis set
hf                     !Perform HF calculation
ccsd(t)                !Perform ccsd(t) calculation

If the same files are used in a subsequent calculation, MOLPRO will automatically recover all data saved on the given files. For instance, if the following input is used after the previous example, the integrals and orbitals will be restarted and used for the subsequent casscf and MRCI calculations:

***,title
memory,16,m            !allocate 16 MW of memory
file,1,filename.int    !allocate permanent integral file
file,2,filename.wfu    !allocate permanent wave-function (dump) file
casscf                 !casscf, using previous scf orbitals as starting guess
mrci                   !mrci using casscf reference wavefunction

If only file 2 is defined in the input, the integrals will automatically be recomputed, as in the following input.

***,title
memory,16,m            !allocate 16 MW of memory
file,2,filename.wfu    !allocate permanent wave-function (dump) file
casscf                 !casscf, using previous hf orbitals as starting guess
mrci                   !mrci using casscf reference wavefunction

The automatic restart mechanism can be disabled by specifying new after the filename(s), e.g.,

***,title
memory,16,m                !allocate 16 MW of memory
file,2,filename.wfu,new    !allocate a new permanent wave-function (dump) file. 
                           !If the file exists, overwrite it.
hf                         !Perform hartree-Fock calculation
casscf                     !casscf, using hf orbitals as starting guess