The level occupations are not negative as seen from the eigenvalues. Some of the matrix elements are negative but this only tells the relative sign of the atomic orbitals components in the occupied states
stefano (sent from my phone) > On 22 Mar 2016, at 07:54, Mostafa Youssef <[email protected]> wrote: > > Dear all, > > I'm relaxing the structure of rutile TiO2 using ultrasoft pseudopotentials > for Ti and O and PBEsol + U with U=5 eV on Ti. For that purpose I use > occupations = 'fixed'. But I found that one of the Ti ions has negative > occupations. To me this looks a bit strange since I'm not using any smearing. > The same result can be obtained by another set of PP. Improving the cutoffs > or the k-point sampling does not resolve the problem. Any thoughts about the > reason and possible remedies are appreciated. I copy below the occupation > matrices for the two Ti ions in the cell and the input file. > > > Thank you, > Mostafa Youssef > MIT > > The matrices are: > > atom 1 Tr[ns(na)] = 2.70769 > eigenvalues: > 0.142 0.177 0.182 0.417 0.436 > eigenvectors: > 0.675 0.000 0.000 0.325 0.000 > 0.000 0.000 0.500 0.000 0.500 > 0.000 0.000 0.500 0.000 0.500 > 0.000 1.000 0.000 0.000 0.000 > 0.325 0.000 0.000 0.675 0.000 > occupations: > 0.231 0.000 0.000 0.000 -0.129 > 0.000 0.309 -0.127 0.000 0.000 > 0.000 -0.127 0.309 0.000 0.000 > 0.000 0.000 0.000 0.177 0.000 > -0.129 0.000 0.000 0.000 0.328 > atom 2 Tr[ns(na)] = 2.70768 > eigenvalues: > 0.142 0.177 0.182 0.417 0.436 > eigenvectors: > 0.675 0.000 0.000 0.325 0.000 > 0.000 0.000 0.500 0.000 0.500 > 0.000 0.000 0.500 0.000 0.500 > 0.000 1.000 0.000 0.000 0.000 > 0.325 0.000 0.000 0.675 0.000 > occupations: > 0.231 0.000 0.000 0.000 0.129 > 0.000 0.309 0.127 0.000 0.000 > 0.000 0.127 0.309 0.000 0.000 > 0.000 0.000 0.000 0.177 0.000 > 0.129 0.000 0.000 0.000 0.328 > N of occupied +U levels = 5.415371 > > The input file: > &CONTROL > calculation = 'vc-relax' , > verbosity = 'high' , > restart_mode = 'from_scratch' , > outdir='./' , > pseudo_dir = './' , > tstress = .true. , > tprnfor= .true. , > nstep = 2000 , > etot_conv_thr = 1.0D-7 , > forc_conv_thr = 4.0D-5 , > / > &SYSTEM > ibrav = 0 , > nat = 6 , > ntyp = 2 , > nbnd = 48 , > ecutwfc = 45 , > ecutrho = 360 , > nosym =.true. > occupations = 'fixed', > lda_plus_u = .true., > Hubbard_U(1) = 5.0 , > Hubbard_U(2) = 0.0 , > / > &ELECTRONS > diagonalization='david', > mixing_mode = 'plain' , > mixing_beta = 0.7, > startingwfc = 'random', > conv_thr = 1.0d-8 , > / > &ions > ion_dynamics='bfgs' > / > &CELL > cell_dynamics = 'bfgs' , > cell_dofree = 'shape', > press_conv_thr = 0.5 , > / > CELL_PARAMETERS angstrom > 4.6320252669841118 0.0000000000000000 0.0000000000000000 > 0.0000000000000000 4.6320252669841118 0.0000000000000000 > 0.0000000000000000 0.0000000000000000 2.9608930000414442 > ATOMIC_SPECIES > Ti 47.867 ti_pbesol_v1.4.uspp.F.UPF > O 15.9994 o_pbesol_v1.2.uspp.F.UPF > ATOMIC_POSITIONS crystal > Ti 0.0000000000000000 0.0000000000000000 0.0000000000000000 > Ti 0.5000000000000000 0.5000000000000000 0.5000000000000000 > O 0.3048741584772117 0.3048741584772117 0.0000000000000000 > O 0.6951258415227883 0.6951258415227883 0.0000000000000000 > O 0.8048741584772117 0.1951258415227883 0.5000000000000000 > O 0.1951258415227883 0.8048741584772117 0.5000000000000000 > K_POINTS automatic > 4 4 6 1 1 1 > > _______________________________________________ > Pw_forum mailing list > [email protected] > http://pwscf.org/mailman/listinfo/pw_forum
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