`Problem:`- The SURF calculation crashes with an error message like
?ERROR IN VIRTORB: INCORRECT NUMBER OF ORB... ERROR EXIT CURRENT STACK: MAIN

`Solution:`- The program has problems in the symmetry conversion when restarting
a Hartree-Fock calculation from the reference calculation at the
equilibrium geometry. You need to start the Hartree-Fock
calculations independently by using the keywords
`start,atden`.

`Problem:`- In parallel calculations (MPPX) the CPU-time of a
`SURF`calculation differs considerably from the real-time (wallclock time). `Solution:`- There may be two reasons for this: (1) Usually a
`SURF`calculation spends a significant amount of the total time in the Hartree-Fock program and the 2-electron integrals program. As the integrals are stored on disk, 2 processes on the same machine may write on disk at the same time and thus the calculation time depends to some extend on the disk controller. It is more efficient to stripe several disks and to use several controllers. This problem can be circumvented by distributing the job over several machines, but limiting the number of processors for each machine to 1. (2) The integrals program buffers the integrals. Parallel jobs may require too much memory (factor of 2 plus the shared memory) and thus the integrals buffering will be inefficient. Try to reduce the memory as much as you can. It might be advantageous to separate the memory demanding`VCI`calculation from the`SURF`calculation.

molpro@molpro.net 2019-06-17