[Pw_forum] PW.x homogeneous electric field berry phase calculation in trigonal cell

[Lorenzo Paulatto]

To be honest I do not remember, what I rmember is that if the field is not 
along z (or the third axis) then it will have (had?) a huge bottleneck in 
parallel which will make it unusable with more than a couple of cpus. 
hth

On Tuesday, February 7, 2017 5:09:03 PM CET Louis Fry-Bouriaux wrote:
> Hi there,
> 
>     I am trying to perform a berry phase calculation with a homogeneous electric 
field (lelfield=.true.) however I receive the "wrong k-strings?" in c_phase error while 
running in parallel with OpenMPI on 4 processors:
> >From the documentation, if K_POINTS is automatic, then field strength
> >should be specified in cartesian coordinates (efield_cart(i)) and 'efield'
> >is not used, however reading the berry phase documentation says that the
> >direction of the efield is taken along gdir when a homogeneous electric
> >field is applied.
> Must I still specify efield_cart values when gdir is specified (it would
> seem so)? The code doesn't complain until after bandstructure computation.
> I have tried efield calculation with the following specification (see below
> for input file used):
> 
> 
> efield_cart(1) = 0.0001,
> 
> efield_cart(2) = 0,
> 
> efield_cart(3) = 0,
> 
> 
> which results in the electric field existing in two directions in crystal
> reference system, but the error is the same whether I do or do not include
> these fields and leave efield=0.0001
> 
> 
> My process is as follows:
> 
>  - scf calculation of trigonal alpha-Al2O3 cell (input crystal is correct)
> 
>  - band structure calculation
> 
>  - Berry phase calculation *without* electric field (this works and output
> is correct) with input:
> 
> 
>  &CONTROL
>                        title = 'alpha-Alumina' ,
>                  calculation = 'nscf' ,
>                       outdir = '${PWD}' ,
>                   pseudo_dir = '${PWD}/pseudo/' ,
>                    verbosity = 'high' ,
>                       prefix = 'run_${RUN_NUMBER}',
>                       lberry = .true.,
>                         gdir = 1,
>                       nppstr = 10,
>                     lelfield = .false.,
>                    nberrycyc = 1
>  /
>  &SYSTEM
>                        ibrav = 5,
>                            A = 5.136,
>                        cosAB = 0.56956647115,
>                          nat = 10,
>                         ntyp = 2,
>                  occupations = 'fixed',
>                      ecutwfc = 50,
>                      ecutrho = 350,
>                         nbnd = 48
>  /
>  &ELECTRONS
>                     conv_thr = 1d-8,
>              diagonalization =  'cg',
>                  mixing_beta = 0.7,
>             electron_maxstep = 200,
>                       efield = 0,
>                 efield_phase = 'write'
>  /
> ATOMIC_SPECIES
>     O   15.99900   O.pbe-van_ak.UPF
>    Al   26.98200   Al.pbe-n-van.UPF
> ATOMIC_POSITIONS crystal
>     O      0.556000000    0.944000000    0.250000000
>     O      0.444000000    0.056000000    0.750000000
>     O      0.250000000    0.556000000    0.944000000
>     O      0.750000000    0.444000000    0.056000000
>     O      0.944000000    0.250000000    0.556000000
>     O      0.056000000    0.750000000    0.444000000
>    Al      0.352000000    0.352000000    0.352000000
>    Al      0.648000000    0.648000000    0.648000000
>    Al      0.148000000    0.148000000    0.148000000
>    Al      0.852000000    0.852000000    0.852000000
> K_POINTS automatic
>   10 4 4   0 0 0
> 
> - Then Berry phase calculation *with* electric field:
> 
> 
>  &CONTROL
>                        title = 'alpha-Alumina' ,
>                  calculation = 'nscf' ,
>                       outdir = '${PWD}' ,
>                   pseudo_dir = '${PWD}/pseudo/' ,
>                    verbosity = 'high' ,
>                       prefix = 'run_${RUN_NUMBER}',
>                       lberry = .true.,
>                         gdir = 1,
>                       nppstr = 10,
>                     lelfield = .true.,
>                    nberrycyc = 1
>  /
>  &SYSTEM
>                        ibrav = 5,
>                            A = 5.136,
>                        cosAB = 0.56956647115,
>                          nat = 10,
>                         ntyp = 2,
>                  occupations = 'fixed',
>                      ecutwfc = 50,
>                      ecutrho = 350,
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