[Pw_forum] Regarding structural optimization
Dear Sir, (1) Here i am running Black phosphorous, which is layered compound crystallizes in orthorhombic structure and reported that having huge van der waals forces. Generally systems having van der waals forces shows huge 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 up to 10e-8 . Where as in "vc-relax" calculations i got 10% volume change with experimental volume. 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. (2) What is the difference in structural optimization between normal process( optimizain c/a, b/a and a with energy) and "vc-relax"? Thanks in advance. with regards S.Appalakondaiah Research scholar University of Hyderabad Hyderabad -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110921/1166c7a0/attachment.htm
[Pw_forum] regarding structural optimization
Because of your question without any details, I can only answer it generally. For getting convergency lattice parameter by energy-volume method, you can read the paper,Acta Materialia 54 (2006) 1641-1657, in which the author discussed that issue by Wien2k code. Or, if you want to use "vc-relax", you'd better decrease the convergence threshold to very small number with convergence cutoff energy, k-mesh and so on. One more to be noted is that the minimum energy configuration corresponds to zero force, but minimum enthalpy corresponds to zero force and stress. In "vc-relax" case, we try to find zero both for force and stress instead of only for total energy. -- GAO Zhe CMC Lab, MSE, SNU, Seoul, S.Korea At 2011-09-14 17:14:08,"kondaiah samudrala" wrote: Dear all, I am doing test calculations for orthorhombic layered compounds having van der waals forces. i calculated the volume by varying c/a, b/a and a with energy and taken the minimum values of c/a, b/a and a. But my volume change is surprisingly 2% with experimental ( even van der waals forces having). I tried with the "vc-relax" for same system i found 12% volume change with experimental.I tried with psedopotentials also and the results are same. I am very thankful any to solve this problem. Thanks in advance S.Appalakondaiah Research Scholar University of hyderabad Hyderabad India -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110916/3bc17b0d/attachment.htm
[Pw_forum] regarding structural optimization
Dear all I am doing test calculations for orthorhombic layered compounds having van der waals forces. i calculated the volume by varying c/a, b/a and a with energy and taken the minimum values of c/a, b/a and a. But my volume change is surprisingly 2% with experimental ( even van der waals forces having). I tried with the "vc-relax" for same system i found 12% volume change with experimental.I tried with psedopotentials also and the results are same. I am very thankful any to solve this problem. Thanks in advance S.Appalakondaiah Research Scholar University of hyderabad Hyderabad India
[Pw_forum] regarding structural optimization
Dear all, I am doing test calculations for orthorhombic layered compounds having van der waals forces. i calculated the volume by varying c/a, b/a and a with energy and taken the minimum values of c/a, b/a and a. But my volume change is surprisingly 2% with experimental ( even van der waals forces having). I tried with the "vc-relax" for same system i found 12% volume change with experimental.I tried with psedopotentials also and the results are same. I am very thankful any to solve this problem. Thanks in advance S.Appalakondaiah Research Scholar University of hyderabad Hyderabad India -- next part -- An HTML attachment was scrubbed... URL: http://www.democritos.it/pipermail/pw_forum/attachments/20110914/62e67db8/attachment.htm
