Periodicity?

Message

Lecuyern · #1 Post by **Lecuyern** » Fri Sep 14, 2007 1:18 pm

Hi everyone!

In order to make some tests I tried to do modelling of a single H2 molecule in a square box of 10Ang.

Depending of its position in the box, the energy of H2 changes after optimization. The energy difference is about 0,0005eV.

Since this is a periodic system, why isn't the energy the same wherever H2 is in the box?

#2 Post by **admin** » Mon Sep 17, 2007 10:59 am

1) the results should be independent of the position of H2 in the box. Please check whether
--) the difference is significant at all (ionic and electronic convergence criteria)
--) you chose the correct KPOINTS (Gamma only)
--) the symmety analysis obtained equal results

Lecuyern · #3 Post by **Lecuyern** » Tue Sep 18, 2007 12:37 pm

Thanks for the answer.

Just to make sure I understand your second point:

By choosing the correct KPOINT "gamma only", do you mean to specify Gamma on the third line of the KPOINT file?

#4 Post by **admin** » Tue Sep 25, 2007 10:48 am

simply give a 1x1x1 MP mesh, this generates exactly the gamma point