Dear Javier, For spin-polarized case, you have 0.6698526-1.0038673=-0.3340147, value very similar to the spin unpolarized case. Polarization is defined only modulo a quantum, and in the above, I just subtracted the quantum.
Andrei On Fri, Feb 20, 2015 at 10:27 AM, Nossa, Javier <[email protected]> wrote: > Dear pwscfers, > I am calculating the polarization of BaTiO3 and found a different value of > it when implementing spin-polarized, nspin=2. > > non-spin-polarized gives P=-0.3340199 (mod 2.0077346) C/m^2, which is > correct. > spin-polarized gives P=0.6698526 (mod 1.0038673) C/m^2, which is not > correct. > > Although it seems to be just a factor of two difference in the absolute > value of the polarization, it is not exactly a factor of two. It is > 2.0054... > In addition, the sign of the polarization is opposite. > On the other hand, the mod is exactly a factor of two. > > Why there is such a difference in the polarization? > > I am doing this as a test because my real system is magnetic and bigger > than BaTiO3. > > Here are the inputs for the nscf calculation: > > spin-polarized: > &control > calculation='nscf' > restart_mode='from_scratch', > prefix='job', > lberry = .true. > gdir = 3 > nppstr = 10 > / > &system > ibrav= 0, > celldm(1)=1.0, > nat= 5, ntyp= 3, > ecutwfc = 120, > !occupations='smearing', smearing='gauss', degauss=0.003, > !occupations='fixed', > input_dft='wc' > nspin=2, > tot_magnetization= 0.0, > / > &electrons > / > ATOMIC_SPECIES > Ba 137.327 Ba.wc-n-nc.UPF > Ti 47.867 Ti.wc-n-nc.UPF > O 15.9994 O.wc-nc.UPF > CELL_PARAMETERS (alat=1.0) > 7.54662 0.0 0.0 > 0.0 7.54662 0.0 > 0.0 0.0 7.74409 > ATOMIC_POSITIONS {crystal} > Ba 0.00000 0.00000 0.00000 > Ti 0.50000 0.50000 0.48186 > O 0.00000 0.50000 0.51791 > O 0.50000 0.00000 0.51791 > O 0.50000 0.50000 0.03133 > K_POINTS {automatic} > 4 4 4 0 0 0 > > > non-spin-polarized: > &control > calculation='nscf' > restart_mode='from_scratch', > prefix='job', > lberry = .true. > gdir = 3 > nppstr = 10 > / > &system > ibrav= 0, > celldm(1)=1.0, > nat= 5, ntyp= 3, > ecutwfc = 120, > !occupations='smearing', smearing='gauss', degauss=0.003, > !occupations='fixed', > input_dft='wc' > / > &electrons > / > ATOMIC_SPECIES > Ba 137.327 Ba.wc-n-nc.UPF > Ti 47.867 Ti.wc-n-nc.UPF > O 15.9994 O.wc-nc.UPF > CELL_PARAMETERS (alat=1.0) > 7.54662 0.0 0.0 > 0.0 7.54662 0.0 > 0.0 0.0 7.74409 > ATOMIC_POSITIONS {crystal} > Ba 0.00000 0.00000 0.00000 > Ti 0.50000 0.50000 0.48186 > O 0.00000 0.50000 0.51791 > O 0.50000 0.00000 0.51791 > O 0.50000 0.50000 0.03133 > K_POINTS {automatic} > 4 4 4 0 0 0 > > > Pseudopotentials are taken from THEOS PSLibrary 0.3.1. > > Outputs are attached. > > > Thank you very much for your help. > > -- > With best regards, > Javier Francisco Nossa > > Postdoc at Geophysical Laboratory > Carnegie Institution of Washington > 5251 Broad Branch Road, N.W. > Washington, DC 20015-1305 > Tel.: 1.240.476.3993 > E-mail: [email protected] <[email protected]> > > _______________________________________________ > Pw_forum mailing list > [email protected] > > https://urldefense.proofpoint.com/v2/url?u=http-3A__pwscf.org_mailman_listinfo_pw-5Fforum&d=AwICAg&c=-dg2m7zWuuDZ0MUcV7Sdqw&r=iaCUSkNPjaS0OZmx8CL3zuFJHmomB6kEDsD3Du2Xz38&m=jHc1e4BMDezKEN4w-4Sz3WYY43oEOCVzdofkatuhMr0&s=ptunJ7qbTZCjdsr3TWNH3-Yh3KVY76v7PTd5Aj-blsQ&e= > -- Andrei Malashevich Postdoctoral Associate Center for Research on Interface Structures and Phenomena Department of Applied Physics Yale University
_______________________________________________ Pw_forum mailing list [email protected] http://pwscf.org/mailman/listinfo/pw_forum
