[Pw_forum] cell optimization

[hania djani-ait aissa]

dear users,
I am trying to optimize lattices parameters in tetragonal centered structure. putting c/a=cte and a=7.28, 7.29, 7.30 ......7.36, I've got the results on total energy: 
 
a=7.28    E=-1282.635
a=7.29    E=-1282.639
a=7.30    E=-1282.658
a=7.31    E=-1282.684
a=7.32    E=-1282.654
a=7.33    E=-1282.624
a=7.34    E=-1282.679
a=7.35    E=-1282.669
a=7.36    E=-1282.652
I've done the calculations twice and in each case convergence is well achieved giving same results.
so, why above a=7.31, total energy rises and drops. is it because ecutoff is too small? (ecutoff=25Ry)
thanks a lot for any answer.
 
Hania Djani-AitAissa
Center of development of advanced technologies, Algiers, Algeria
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