[molpro-user] Diffrerence between molpro and mrcc fci

[Cong Wang]

Hi everyone,

  I tried to compare molpro and mrcc full-ci/cc-pVDZ for a lithium atom and
posted my question on mrcc forum.

The molpro convergence pattern is

  1   1    0.6  1.00000000    -7.43241988
                                           0.03 -0.00020840 -0.00020768
  2   1    0.6  0.00860636    -7.43263477
                                           0.05 -0.00000213 -0.00000210
  3   1    0.6  0.00085487    -7.43263690
                                           0.09 -0.00000004 -0.00000003
  4   1    0.6  0.00009565    -7.43263693
                                           0.11 -0.00000000 -0.00000000
  5   1    0.6  0.00001648    -7.43263693
                                           0.10 -0.00000000 -0.00000000
  6   1    0.6  0.00000299    -7.43263693
                                           0.12 -0.00000000 -0.00000000
  7   1    0.6  0.00000052    -7.43263693
                                           0.11 -0.00000000 -0.00000000
  8   1    0.6  0.00000010    -7.43263693

mrcc is

 Iteration  8  CI energy:    -7.43263751  Energy decrease:   0.0000E+00
 ======================================================================
 Norm of residual vector:     1.0477E-12      Convergence:   5.1862E-12
 CPU time [min]:     0.012                   Wall time [min]:     0.002

 Iteration  9  CI energy:    -7.43263751  Energy decrease:   0.0000E+00
 ======================================================================
 Norm of residual vector:     4.7386E-14      Convergence:   2.1137E-13
 CPU time [min]:     0.013                   Wall time [min]:     0.002

 Iteration 10  CI energy:    -7.43263751  Energy decrease:   0.0000E+00
 ======================================================================
 Norm of residual vector:     1.8060E-15      Convergence:   1.2633E-14
 CPU time [min]:     0.014                   Wall time [min]:     0.002

 Iteration 11  CI energy:    -7.43263751  Energy decrease:   0.0000E+00


Though I was suggested to tighten molpro convergence threshold, my input:
{fci;thr,1d-16;core,0}
and convergence pattern seems unable to reach mrcc value. Hence, I would
like to ask in this mailing list, what is the actual reason for this
discrepancy? i.e.
  -7.43263693
  -7.43263751

Thank you
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