Dear experts, I need to get the optimal number of layers of (110) niobium that is a good representative of the behavior of the material, but I am facing the following problems:
1. I Keep getting the following warning when relaxing the bulk material: "SCF correction compared to forces is large: reduce conv_thr to get better values" I tried reducing conv_thr, increasing ecutwfc and/or K-mesh, and occupations, but no success yet ( the set up I am using for this calculation is given below) 2. the surface energy I get from the (110) slab I cleave from this bulk structure is significantly increasing with increasing number of layers : [ 3L : 0.13814157, 5L :0.14193375, 7L :0.14578974, 9L : 0.15090349, 11L : 0.1554551 , 13L : 0.16026892] // [eV/\AA^2] I am wondering whether I am having a problem with the bulk or my surface calculations or even the PP I am using ( I need to keep using NCPP as I am going to look into phonon bands), Thank you for your help, Roozbeh PDF, Physics, Queen's University , Canada // input file for bulk : &CONTROL calculation= 'vc-relax', title='ml_gr', prefix='ml_gr', verbosity='high', restart_mode= 'from_scratch', nstep=200, iprint=1, tprnfor=.true., outdir='./tmp', disk_io='default', pseudo_dir='../pp_sg15_oncv/', ! vanderbilt NC PBE, forc_conv_thr=1.0d-6, / &SYSTEM ibrav=0, nat = 2 , ntyp = 1, ecutwfc = 55.0 , ecutrho = 440.0, nosym=.true., occupations='smearing', smearing='cold', degauss=0.02, vdw_corr='grimme-d3', input_dft='PBE', / &ELECTRONS startingwfc='random', diagonalization='cg', conv_thr = 1.0e-12, mixing_beta = 0.2, electron_maxstep=200, / &IONS ion_dynamics='bfgs', upscale=20.0, / &CELL press_conv_thr = 0.5D0, press = 0.D0, cell_dynamics = 'bfgs', cell_dofree = 'all', cell_factor = 1.5D0, / ATOMIC_SPECIES Nb 92.906 Nb_ONCV_PBE-1.2.upf ! [Kr] 4d4 5s1, K_POINTS automatic 12 12 12 0 0 0 CELL_PARAMETERS (angstrom) 3.3205199242 0.0000000000 0.0000000000 0.0000000000 3.3205199242 0.0000000000 0.0000000000 0.0000000000 3.3205199242 ATOMIC_POSITIONS (crystal) Nb 0.000000000 0.000000000 0.000000000 Nb 0.500000000 0.500000000 0.500000000
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