Dear Andrei and Marcos, Nothing changed appreciably, so i need to test for semicore in La.
Thank you very much for your suggestions. 1009u 2009/12/14 Marcos Veríssimo Alves <marcos.verissimo.al...@gmail.com> > Hi Sonu, > > So what was the change in the results with the stronger relaxation and > smaller displacement for the force constant matrix calculation? If nothing > has changed appreciably, then indeed you should test for semicore in La, as > Andrei says. Again, if nothing has changed appreciably in your results, at > least you have ruled out the easiest possible elements to be checked for > (since generating a new pseudo is often boring work)... And most likely you > can do the calculations with semicore using the same higher (0.01 eV/Ang) > force tolerance as before, because your calculations will become a bit > heavier with semicore. > > Cheers, > > Marcos > > > On Mon, Dec 14, 2009 at 9:07 AM, <apost...@uni-osnabrueck.de> wrote: > >> > Dear Andrei and Marcos, >> > >> > 1) As a DFT problem, i used La in its +3 state along with non-linear >> core >> > correction with pseudocore, Not semocore >> > states. >> > La(+3) PP gen configuration is : >> > 5s2 1.83 >> > 5p6 2.19 >> > 5d0 3.00 >> > 4f0 1.25 with pseudocore radius 1.50 bohr. >> > >> > I think i need to change pseudocore ? Please give suggestions over >> > this why i should increase or decrease the pseudocore? >> >> I did not spoke about pseudocore, but about semicore, meaning, 5p. >> You include 5s and 5p in the valence; this is probably OK. >> I calculated something containing La with 5s in the core, >> being somehow afraid of a too much ionized +3 configuration, >> but this was not a priori better. You should test. >> >> > how it can affect the frequencies? >> >> Who knows? In principle, the semicore (and also pseudocore) stuff >> often has effect on elastic properties, even if you'll see no changes >> in the electronic structure. >> >> > 2) I used FC Displ= 0.005Bohr, hopefully within harmonic approximation. >> >> This is not really the point. For some modes this number won't affect >> anything at all, and for others, where anharmonicity is important, it will >> change quite a lot. But for such anharmonic modes, also the experimental >> data may be ambiguous, and at least depend on temperature. >> You objective is not to get the best agreement with SOME experiment, >> but provide a consistent and reliable und understandable result. >> If at the end your frequency comes 200 cm-1 off, but you are sure >> that it is the "DFT truth" and not due to some stupid mistake, - >> so is life... Someone else can be able to explain it... >> >> > 3) I Relaxed the system with MaxForceTol= 0.0001 ev/Ang. >> >> This parameter is rarely a reason to worry, once you are safe on what >> regards the MeshCutoff. Even if your starting point for phonon >> calculations is not exactly at the eauilibrium, but close enough to it, >> it won't be a problem to get good force constants (because of the way >> they are evaluated). >> >> > 4) Can SIESTA calculates bulk modulus directly? >> >> No >> >> > or do i need to calculate it through fitting process using Murnaghan >> > equation of state? >> >> Yes (or so I think) >> >> Best regards >> >> Andrei Postnikov >> >> >> > -- 1009U
