Dear Sir,<br><br> Thank you for your reply. I am sorry for not sending
complete details. Here i am running Black phosphorous, which is layered
compound and reported that havng huge van der waals forces. Genarally
systems having van der waals forces shows volume change( either 10-12%
underestimate in LDA or 5-6% overestimate in GGA) with experimental
volume in DFT calculations. In my case,CASTEP and VASP i got similar
variation in volume. But in PwSCF, i got 2% volume change with
experimental volume. Here i used 50Ry cutoff and 10X10X10 K-mesh is used
for my calculations. For energy minimum i used upto 10e-8 .Where as in
"vc-relax" calculations i got 10% volume change with experimental
volume.<br>
<br> please give your suggestions for my problem. If it is need i will
send my b/a, c/a and a calculation input and output files to your mail.<br><br>with regards<br>S.Appalakondaiah<br>Research scholar<br>University of Hyderabad<br>
Hyderabad