[molpro-user] relaxed Pople cluster corrections

[harding]

  I believe the relaxed Pople cluster corrections coming out of Molpro 
are incorrect.

  If I do the following calculation using Molpro 2010.1 :

memory,20,m
geometry={
  C }

basis=vtz

{multi
occ,2,1,1,0,1,0,0,0
closed,1,0,0,0,0,0,0,0
wf,6,4,2}

{ci}

I get the following results:

  Coefficient of reference function:   C(0) = 0.98244004 (fixed) 
0.98247737 (relaxed)
  Reference energy                     -37.70568461
  Correlation energy                    -0.07384460
  !MRCI STATE 1.4 Energy               -37.779529217128

  Cluster corrected energies           -37.78219258 (Davidson, fixed 
reference)
  Cluster corrected energies           -37.78218676 (Davidson, relaxed 
reference)

  Cluster corrected energies           -37.78086047 (Pople, fixed reference)
  Cluster corrected energies           -37.77952922 (Pople, relaxed 
reference)

  Note that the relaxed Pople cluster corrected energy is identical to 
the uncorrected CI energy.

  I can reproduce the fixed and relaxed Davidson results using the 
equations in section 20.7 of the Molpro manual. As an aside I note that 
there appears to be a numbering inconsistency in the manual as the 
equation numbers in Table 9 do not correspond to those in the text.

I can reproduce the fixed Pople correction using equation 65 from Pople, 
Seeger and Krishnan IJQC, s11, 149 (1977) with n=4. If I use the same 
equation and just replace the fixed C0 with the relaxed C0 listed above 
I get a relaxed Pople cluster corrected energy of,

-37.78085755

not the value shown above.

Am I doing something wrong here or is Molpro in error ?

Larry Harding