[QE-users] SCF convergence of cp.x vs. pw.x

[Giuseppe Mattioli]

Dear Chris
scf convergence with cp.x actually used to be painfully slow! For this  
reason, pw.x and cp.x should be interoperable, that is, you should be  
able to restart a converged pw.x calculation with cp.x. Have a look  
into the CPV/Restart_example/ directory, where restart details are  
explained.
HTH
Giuseppe

Quoting Christoph Wolf <wolf.christoph at qns.science>:

> Dear all,
>
> I am trying to run an SCF calculation in cp.x (because I want to use the
> spin contamination analysis of cp.x), however reaching convergence with
> cp.x seems painfully slow - probably my fault as I am not familiar with
> cp.x.
>
> System is a spin polarized calculation for a molecule in a vacuum box. The
> SCF calculation converges in 30 steps:
>
> !    total energy              =    -813.86536682 Ry
>      Harris-Foulkes estimate   =    -813.86536682 Ry
>      estimated scf accuracy    <          1.3E-11 Ry
>
> But the cp.x calculation is still running after 2000 steps
>
> 1997    0.000605472420187    0.0    0.00    -406.607110121158
>  1998    0.000604666115183    0.0    0.00    -406.607351342414
> 1999    0.000603861731893    0.0    0.00    -406.607592243454
> ...
>
> (NB: the energy difference between CP and PW at this point is ~0.650182333
> Ry)
>
> I am running the cp.x calculation with
>
> calculation = 'scf'
> and electron_dynamics = 'damp
>
> Is that the right way to do this? If yes, am I missing some critical
> parameters for improving convergence?
>
> I attached my input below - any help is much appreciated!
>
> Best,
> Chris
>
> &CONTROL
>   calculation = "scf"
>   prefix = "fepc"
>   pseudo_dir = "/home/chwolf/Work/DFT/00_pseudo/"
>   outdir = "tmp"
>   wf_collect = .true
>   tprnfor = .true.
>   restart_mode = "from_scratch"
>   nstep      = 2000
> /
> &SYSTEM
>    ibrav = 0
>    nat  = 57
>    ntyp = 4
>    nspin = 2
>    occupations = "fixed"
>    ecutwfc = 60
>    ecutrho = 240
>    tot_magnetization=1
>    tot_charge=-1
>    starting_magnetization(1) = 0.5
>    starting_magnetization(2) = 0.0
>    starting_magnetization(3) = 0.0
>    starting_magnetization(4) = 0.0
>    nr1b=24, nr2b=24, nr3b=12
> /
> &ELECTRONS
>   conv_thr=1e-10
>   electron_maxstep = 350
>   electron_dynamics = 'damp'
> /
>
> CELL_PARAMETERS angstrom
> 29.47070000000000 0.00000000000000 0.00000000000000
> 0.00000000000000 29.47070000000000 0.00000000000000
> 0.00000000000000 0.00000000000000 15.000
>
> ATOMIC_SPECIES
> Fe    55.9330    Fe_ONCV_PBE_sr.upf
> C     12.0107    C_ONCV_PBE_sr.upf
> N     14.0067    N_ONCV_PBE-1.0.upf
> H      1.0000    H_ONCV_PBE_sr.upf
>
> ATOMIC_POSITIONS angstrom
> ...
> ..
>
> --
> IBS Center for Quantum Nanoscience
> Seoul, South Korea



GIUSEPPE MATTIOLI
CNR - ISTITUTO DI STRUTTURA DELLA MATERIA
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E-mail: <giuseppe.mattioli at ism.cnr.it>