I would not bother too much about B', but B is changing by 20 %, which is too much.
You have to analyse your data to find out where your error is. Maybe in one set of calculations you have not got the optimized c/a ratio (and corresponding energy) for each volume ??? PS: 5 points are probably ok for equillibrium V and c/a, but B will always have quite some error. Spin-orbit: Emax in case.in1 should be increased. Emax in case.inso can stay at eg. 1.5 Ry You don't need to worry about "qtl-B" at very high (unoccupied) energies (unless for some spectroscopy you need these high states). Am 30.07.2012 06:15, schrieb Vinayak Mishra: > I have basically two questions to ask. I will like to mention that I > have gone through the related previous questions and their answers on > registered users site. I will be highly obliged if you could kindly > spare some time to go through the following two queries. > > 1.) I was doing c/a optimization at five different volumes in bct > structure for a particular case and was trying to get equilibrium > volume and tentative value of bulk modulus and its pressure > derivative. I gave optimization for one set of 5 volumes, say +5.0, > 0.0, -5.0, -10.0, -15.0 and another set, say +5.5, 0.5, -5.5, -10.5, > -15.5 and then get EOS, then I find that there is a huge difference > in the value of pressure derivative of bulk modulus K? for the two > cases. I have plotted both the cases together in the plot.ps file > attached herewith. Here in the plot ?E? is the same constant value of > energy for both the curves. Only thing is, for the sake of clarity of > seeing the two curves together, in the solid curve 0.001 Ryd of energy > is added so that it is shifted up by that much energy so that one can > see the difference between the shape of two curves clearly. Both the > curves as such don?t seem to be much different, then why such a large > difference in K?. Even otherwise also, why should it matter whether > the run is given for 1st set of volumes or the 2nd set of volumes. > Could you please comment on this Prof. Blaha? > > 2.)While doing a spin-orbit calculation, we need to increase Emax upto > 10 Ry in case.in1 file even though we are interested in eigenvalues > near Fermi energy. But as said in users guide, in the > "second-variation" these high eigenstates form the basis functions > for the SO calculation. Without these high eigenvalues there will be a > poor basis even for states near Fermi energy.. But these high > eigenvalues are giving large QTL-B value of 980 or 1500 value, at high > energies say around 4.0 in case.output2 file if emax is set as 5.0 > (instead of the default value 1.5) in case.inso file also apart from a > Emax=5 (default in SO calculations) in case.in1 file, when we try to > calculate partial charges by giving the command 'x lapw2 -so -qtl'. > After this, the command 'x tetra' is given to get density of states. > So as said earlier, this is so when case.inso file also has emax = 5.0 > i.e the maximum energy for which output eigenvectors and eigenenergies > will be printed (p.96 of users guide). But if we put emax =1.5, which > is the default value in case.inso file, then anyway at high energies > no computation of eigenvectors and eigen energies is done and no such > statement appears in the case.output2 file. It is true that fermi > energy is far below the energy level at which high QTL-B is quoted in > case.output2 file. My question here is: How and where Emax = 5.0 of > case.in1 file is used so that getting large qtl-b in output2 while > calculating partial charges, is meaningless or unharmful, if we happen > to keep emax equal to 5.0 in case.inso also. I just want to confirm > that a large qtl-b value at energies 0.5 to 1Ryd higher than Fermi > energy in case.output2 file is harmless and that I can use Emax upto > 10 in case.in1 file without any hesitation. I will highly appreciate > your clarification on this. > > Thank you very much in advance for your attention and time. > > V. Mishra > > > > _______________________________________________ > Wien mailing list > Wien at zeus.theochem.tuwien.ac.at > http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien > -- P.Blaha -------------------------------------------------------------------------- Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna Phone: +43-1-58801-165300 FAX: +43-1-58801-165982 Email: blaha at theochem.tuwien.ac.at WWW: http://info.tuwien.ac.at/theochem/ --------------------------------------------------------------------------
