Hi, I wonder why is the band calculation much longer than a scf calcuation. I did a calculation for a 64-atoms supercell using 20 cpu cores. In summary, I did 1) SCF calculation with only gamma point, run in two minutes. 2) Non-self-consistent band calculation with 27 k-points.
In the nscf calculation each k-point takes 15-20 minutes and the total calculation lasts 7 hours. I understand that for the k-points along the line the wfc are complex, the symmetry is smaller, but even so the time scale is quite different. The machine has to keep all the wfc in memory, but it was not swapping. Even the gamma point took 15 minutes, why does it takes longer than the scf calculation? Please, let me know if I am doing something wrong. Below are the inputs for the scf and the bnd calculations. SCF: &CONTROL calculation = 'scf' restart_mode='from_scratch', pseudo_dir = "./", outdir="./tmp/", tstress = .true., tprnfor = .true. , prefix= 'cdte64', disk_io = 'low', etot_conv_thr = 1.0D-3, wf_collect=.TRUE., verbosity='high' / &SYSTEM ibrav= 1, celldm(1) = 25.02, nat = 64, ntyp = 2, ecutwfc = 28.67, ecutrho = 180, degauss = 0.001D0, occupations = "smearing", smearing = "gauss", tot_charge = 0, nspin = 1 , ! set to 2 for spin polarized ! tot_magnetization = 0 , ! change to 1 / &ELECTRONS diagonalization='david' conv_thr = 1.D-6, mixing_beta = 0.4D0, diago_david_ndim= 2, / &IONS pot_extrapolation='second_order', trust_radius_max = 0.7, trust_radius_ini = 0.7, / ATOMIC_SPECIES Cd 112.411 cd_pbe_v1.uspp.F.UPF Te 127.600 te_pbe_v1.uspp.F.UPF ATOMIC_POSITIONS (alat) Cd 0.5000000000000000 0.5000000000000000 0.5000000000000000 Cd 0.0000000000000000 0.0000000000000000 0.0000000000000000 Cd 0.2500000000000000 0.2500000000000000 0.0000000000000000 …. K_POINTS gamma The NSCF band calculation input is: &CONTROL calculation = 'bands' ! restart_mode='from_scratch', pseudo_dir = "./", outdir="./tmp/", tstress = .true., tprnfor = .true. , prefix= 'cdte64', disk_io = 'low', etot_conv_thr = 1.0D-3, verbosity='high' / &SYSTEM ibrav= 1, celldm(1) = 25.02, nat = 64, ntyp = 2, ecutwfc = 28.67, ecutrho = 180, degauss = 0.001D0, occupations = "smearing", smearing = "gauss", tot_charge = 0, nspin = 1 , ! set to 2 for spin polarized ! tot_magnetization = 0 , ! change to 1 / &ELECTRONS diagonalization='david' conv_thr = 1.D-6, mixing_beta = 0.4D0, diago_david_ndim= 2, / &IONS pot_extrapolation='second_order', trust_radius_max = 0.7, trust_radius_ini = 0.7, / ATOMIC_SPECIES Cd 112.411 cd_pbe_v1.uspp.F.UPF Te 127.600 te_pbe_v1.uspp.F.UPF ATOMIC_POSITIONS (alat) Cd 0.5000000000000000 0.5000000000000000 0.5000000000000000 Cd 0.0000000000000000 0.0000000000000000 0.0000000000000000 Cd 0.2500000000000000 0.2500000000000000 0.0000000000000000 …. K_POINTS crystal_b 3 0.500 0.500 0.500 17 0.000 0.000 0.000 10 0.500 0.000 0.000 1 Thank you. Eduardo Menendez Proupin Departamento de Fisica, Facultad de Ciencias, Universidad de Chile URL: http://www.gnm.cl/emenendez
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