Hi,
I found an odd progression of energies during a NWChem 6.8 EOM-CCSD calculation of naphthalene in Cs symmetry, cc-pvtz basis, no frozen core. The following is from the a' irrep, and focusing on the 4.6 eV root that starts off as root 1.
...
Iteration 38 using 134 trial vectors
0.0000000240613 0.1694889939661 4.61203
...
Iteration 39 using 135 trial vectors
0.0000000240820 0.1694889939566 4.61203
...
Iteration 40 using 136 trial vectors
0.3118749370700 0.0423481583098 1.15235
0.0000000240893 0.1694889939764 4.61203
...
...
Iteration 65 using 193 trial vectors
0.0000000393889 -0.0000000002695 -0.00000
0.0000000327071 -0.0000000002695 -0.00000
0.0000000098575 0.0000000000007 0.00000
0.0000000238503 0.1694889939682 4.61203
0.0000000568039 0.1944784791788 5.29203 1199.3 91.0
--------------------------------------------------------------
Iterations converged
------------------
The root at 4.61203 eV remains in the converged solution, but at iteration 40 shifts to the second root, as the first one plummets toward 0.00000 eV. This happens 2 more times, at iteration 43 (shifts to 3rd root) and iteration 47 (shifts to 4th root). Another program converges with 4.6120 eV as the first root (of course, thresholds may be different).
Any thoughts on whether this should be expected or reflects a problem in the input or code?
TCE input is vanilla,
tce
scf
ccsd
nroots 5
print time tile
end
task tce energy
Thanks; Chris
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