difference between Total energy and ENERGY| Total FORCE_EVAL ( QS ) energy ?
Jun
chen... at googlemail.com
Mon Mar 22 14:22:14 UTC 2010
Hi all,
When doing electronic structure calculations in MD or geo_opt, it is
very often to see a small difference in energy between "Total
energy: **** " and " ENERGY| Total FORCE_EVAL ( QS ) energy
(a.u.): **** " in output files. The difference is usually so small
that I thought it is just due to numerical error. (I am not saying the
difference due to applying some restraining potentials or in MIXED
calculations). However, I recently noticed that the difference can be
as large as 0.1 eV, which makes me wonder what is difference in
definitions of "Total energy " and "ENERGY| Total FORCE_EVAL ( QS )
energy". An example is as follows: (input file (input.inp) is
uploaded)
I have repeated the same ENERGY_FORCE calculation three times (there
may be some differences in the initial guess for wavefunction because
I used SCF_GUESS RESTART.), the energies I got are
1. Total energy:
-3269.58265002363760
ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):
-3269.578462626209330
2. Total energy:
-3269.57862048247534
ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):
-3269.578462728981776
3. Total energy:
-3269.57793566477721
ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.):
-3269.578462722795848
In three cases, " ENERGY| Total FORCE_EVAL ( QS ) energy (a.u.)" are
almost the same, but "Total energy: " are quite different. Especially
for case 1, the difference is up to 0.1 eV.
Any suggestion and comment are appreciated.
Cheers,
Jun
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