[molpro-user] Full CI convergence problems with hydrogen
l.lodi at ucl.ac.uk
Tue Mar 20 12:06:36 GMT 2007
I was trying as a test some FCI calculation for the hydrogen molecule (I
am using molpro v2002.6), but when I try with the aug-cc-pV5Z basis set
I have convergence problems.
This is the input file:
memory, 80, M
r = 0.8
rhf, WF, ELEC=2, SYM=1, SPIN=0
I get a FCI energy of -3.057081385992 hartrees, which is wrong.
On the other hand, if I try with a smaller basis set like aug-cc-pVQZ I
get -1.082735905256 hartrees, which I belive is the correct result for
this basis set.
For values of r greater than 0.9 bohrs everything is OK even with the
A5Z basis set.
Incidentally, I've also tried other methods like MRCI or CCSD but I
always get some errors for some combinations of bond lenghts/basis set.
Is there anything that can be done about this?
N.B.: the calulation FCI(A5Z) takes about 5min of a PC.
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