[molpro-user] disk and memory requirements for MP2

[Gerald Knizia]

On Monday 06 October 2008 16:47, ERSIN YURTSEVER wrote:
> I am running a molpro MP2 calculation of antracene dimer with aug-
> ccpvdz basis.
>
> run stops with
>
> Error writing 32768 words at offset 7482507264. to file21
> implementation=eaf file handle=1 ierr=-1000
>
> ?error
> ?I/O error
> ? the problem occurs in writew
>
> I seem to be running out of disk space.
>
> 1) Did I understand the problem correctly?

Yes, this is the most common cause for this kind of error message.

>  2) is there a way to figure out the necessary disk space (and/or the
>  memory) before doing MP2?

Memory can be specified with memory cards like
	memory,400,m;
at the top of the input file. Note that "m" stands for Mega/word/, which is 
typically 8bytes long. The amount of disk space cannot be configured, but the 
locations where the files are stored can.

>  3) Is it possible to do a calculation restricted to a certain amount
>  of disk?

This is not possible. However, you have two other options:

  1) Use DF-RHF and DF-MP2 or DF-LMP2 instead of canonical Hartree-Fock and 
MP2. These methods are much faster than the canonical ones for large systems 
and require only small amounts of disk space. In MOLPRO, it should be 
sufficient to simply exchange the "hf" commands by "df-hf" and mp2 by 
"df-mp2". For local MP2, see the documentation. If using local methods, you 
should probably use extended domains (iext=1).

  2) Use integral-direct methods. If these are applied, all AO integrals are 
recalculated as required whenever needed and nealy no disk space is required. 
However, this might make calculations rather slow. Also, it is not possible 
for the (T)-triples of CCSD.
-- 
Gerald Knizia