The ABINIT Users Mailing List ( CLOSED )

["Matteo Giantomassi" <Matteo.Giantomassi@uclouvain.be>]

> Hi,
>
> I am trying to run GW calculation for a semiconductor material (Pb Cl I)
> at the gamma point.  However I run into the following error
>
> .....
> ==== Info on the G-sphere ====
>   Number of G vectors ...     1725
>   Number of shells ......      290
>
>  Time reversal symmetry is used
>  Shell   Tot no. of Gs   Cutoff [Ha]
>      1               1        0.000
>      2               3        0.059
>      3               5        0.082
> ......
>   289            1717        5.995
>    290            1725        5.995
>
> setup_coulombian : cutoff-mode = CRYSTAL
>  q-points for optical limit:   1
>      1)      0.000010    0.000020    0.000030
>
>  setup_screening.F90:475:ERROR
>  Mismatch between Dtset%wtk and Kmesh%wt
> -P-0000
> -P-0000  leave_new : decision taken to exit ...
> =========
>
> I am not sure what is the source of this error.  can someone please point
> the reason for this error and any other changes in the input file.

 Dear Anurag,

 You are using kptopt = 0 to specify the k-point sampling.
 In this case, one has to specify the k-point list as well
 as the weight associated to each point. See

 
http://www.abinit.org/documentation/helpfiles/for-v5.8/input_variables/varbas.html#kptopt

 One should always  specify the weights of the k-points calculated taking
into account the symmetry properties of the crystal. Note indeed that,
 if you don't specify wtk in the input file, the weights will be
 initialized to one:

 
http://www.abinit.org/documentation/helpfiles/for-v5.8/input_variables/varbas.html#wtk

 Your input file might introduce innacuracies in the calculations
 of densities and potentials since the contribution
 of each k-point to the density should be weighted according to
 the number of equivalent k-points in the star.

 The GW part reports an error because the weights are always calculated
 taking into the symmetry operations of the system and there's a mismatch
 between the values calculated internally and the corresponding
 values coming from the input file.

 To get rid of the problem, use the standard approach to specify
 the set of k-points.

 kptopt 1 !Take fully into account the symmetry
          ! to generate the k points in the Irreducible Brillouin Zone only
 ngkpt 2 2 4
 shiftk 0.0 0.0 0.0


>  Input
> file is listed below.  I am using ABINIT version 5.8.3 compiled on a Intel
> dual core (dual socket) cluster with Intel 10.1 fortran compilers.
>
> I have two more questions related to GW calculations --
> 1.  how to benefit from band parallelization in GW calculations ?  I know
> we have to set gwpara = 2 but does this in any related to the number of
> processors or bands ?

 This topic has been already discussed on the forum.
 These are the basic rules to be followed in order to achieve
 an optimal distribution of CPU load and memory

 1) For screening calculations, the number of CPUs should ideally
    divide nbands-nocc
 where nbands is the total number of states used to calculate the
polarizability while nocc is the number of occupied bands

 2) For sigma calculation, the optimal load distribution is achieved
    when nbands is divisible by nproc.

>
> 2.  the bottom of conduction band for this compound is slightly offset
> from one of the high symmetry points (it is at (0, 0.4, 0.5)).  In such
> cases how to run GW calculations at such k-points ?  I tried to specify a
> k-point list but I run into error.
>

 Also this topic has been discussed on the forum several times.
 The main difficulty is due to the fact that one can calculate
 GW corrections only for the k-points stored in the KSS file.
 The q-points for the screening file are given by all possible differences
 k1-k2 where k1 and k2 are the points used during the KSS generation.

 Therefore, in order to calculate the QP correction for the bottom of
 conduction, one can generate a new KSS file on a shifted k-mesh, e.g.

 nshiftk 1
 shiftk 0.0 0.4 0.5

 This trick will allow you to reuse the previous screening file.
 without having to run a complete GW calculations from scratch.
 Once you have the KSS file on the shifted mesh, you can run the
 sigma calculation by reading the new KSS file and the old screening file.

 There are other methods you can use to interpolate the GW band structure
 starting from the knowledge of the QP corrections in the irreducible zone.

1) Linear interpolation of the QP corrections as a function
   of the KS energy (E_QP - E_KS is generally linear as a function of
   E_KS)

2) Wannier interpolation of the QP corrections
   See
   
http://www.abinit.org/documentation/helpfiles/for-v5.8/tutorial/lesson_wannier90.html
 and the input file  wannier90/t03.in

 Best Regards,
 Matteo Giantomassi

> thank you for help.
>
> regards,
> Anurag
>
>
>
> ----------- input file --------------
>
> # Crystalline  Pb Cl I   (ICSD #)
> # GW calculation  at Gamma point in reciprocal space (VBM)
> # Dataset 1: ground state calculation # Dataset 2: calculation of the kss
> file
> # Dataset 3: calculation of the screening (epsilon^-1 matrix for W)
> # Dataset 4: calculation of the Self-Energy matrix elements (GW
> corrections)
>
> ndtset 3
>
> #Dataset 1 : usual self-consistent calculation
> # Definition of k-points
> nkpt1   12
> kptopt1 0          # Option for the manual specification of k points,
>      kpt1     0.00000000E+00  0.00000000E+00  0.00000000E+00
>               5.00000000E-01  0.00000000E+00  0.00000000E+00
>               0.00000000E+00  5.00000000E-01  0.00000000E+00
>               5.00000000E-01  5.00000000E-01  0.00000000E+00
>               0.00000000E+00  0.00000000E+00  2.50000000E-01
>               5.00000000E-01  0.00000000E+00  2.50000000E-01
>               0.00000000E+00  5.00000000E-01  2.50000000E-01
>               5.00000000E-01  5.00000000E-01  2.50000000E-01
>               0.00000000E+00  0.00000000E+00  5.00000000E-01
>               5.00000000E-01  0.00000000E+00  5.00000000E-01
>               0.00000000E+00  5.00000000E-01  5.00000000E-01
>               5.00000000E-01  5.00000000E-01  5.00000000E-01
> nbandkss1 120  # number of bands to store in KSS file
> istwfk1  12*1
> prtden1  1         # Print out density
> kssform1 3
>
> # Dataset2: Calculation of the screening (epsilon^-1 matrix)
> optdriver2  3        # Screening calculation
> getkss2     -1       # Obtain KSS file from previous dataset
> nband2      140       # Bands to be used in the screening calculation
> ecutwfn2    6.0      # Planewaves to be used to represent the
> wavefunctions
> ecuteps2    6.0      # Dimension of the screening matrix
> ppmfrq2    18.7 eV  # Imaginary frequency where to calculate the screening
> kptopt2   0
> nkpt2   12
>      kpt2     0.00000000E+00  0.00000000E+00  0.00000000E+00
>               5.00000000E-01  0.00000000E+00  0.00000000E+00
>               0.00000000E+00  5.00000000E-01  0.00000000E+00
>               5.00000000E-01  5.00000000E-01  0.00000000E+00
>               0.00000000E+00  0.00000000E+00  2.50000000E-01
>               5.00000000E-01  0.00000000E+00  2.50000000E-01
>               0.00000000E+00  5.00000000E-01  2.50000000E-01
>               5.00000000E-01  5.00000000E-01  2.50000000E-01
>               0.00000000E+00  0.00000000E+00  5.00000000E-01
>               5.00000000E-01  0.00000000E+00  5.00000000E-01
>               0.00000000E+00  5.00000000E-01  5.00000000E-01
>               5.00000000E-01  5.00000000E-01  5.00000000E-01
> istwfk2  12*1
> #awtr3       0       # Note : the default awtr 1 is better
>
> # Dataset3: Calculation of the Self-Energy matrix elements (GW
> corrections)
> optdriver3  4        # Self-Energy calculation
> getkss3     -2       # Obtain KSS file from dataset 1
> getscr3     -1       # Obtain SCR file from previous dataset
> nband3      100      # Bands to be used in the Self-Energy calculation
> ecutwfn3    5.0      # Planewaves to be used to represent the
> wavefunctions
> ecutsigx3    6.0      # Dimension of the G sum in Sigma_x
>                      # (the dimension in Sigma_c is controlled by npweps)
> nkptgw3      1                # number of k-point where to calculate the
> GW correction
> kptgw3                       # k-points
>  0.000    0.000    0.000    # (Gamma)
> bdgw3       36 37             # calculate GW corrections for bands from 36
> to 37
>
> kptopt3   0
> nkpt3   12
>      kpt3     0.00000000E+00  0.00000000E+00  0.00000000E+00
>               5.00000000E-01  0.00000000E+00  0.00000000E+00
>               0.00000000E+00  5.00000000E-01  0.00000000E+00
>               5.00000000E-01  5.00000000E-01  0.00000000E+00
>               0.00000000E+00  0.00000000E+00  2.50000000E-01
>               5.00000000E-01  0.00000000E+00  2.50000000E-01
>               0.00000000E+00  5.00000000E-01  2.50000000E-01
>               5.00000000E-01  5.00000000E-01  2.50000000E-01
>               0.00000000E+00  0.00000000E+00  5.00000000E-01
>               5.00000000E-01  0.00000000E+00  5.00000000E-01
>               0.00000000E+00  5.00000000E-01  5.00000000E-01
>               5.00000000E-01  5.00000000E-01  5.00000000E-01
> istwfk3  12*1
>
> # Calculation convergence parameter
> toldfe  1.0d-6
>
> # Use only symmorphic operations
> symmorphi 0
>
> gwpara 2
>
> # Definition of the atom types
> ntypat  3         # There are 3 types of atoms
> znucl 82 17 53     # The keyword "znucl" refers to the atomic number of
> the
>                   # possible type(s) of atom. The pseudopotential(s)
>                   # mentioned in the "files" file must correspond
>                   # to the type(s) of atom.
>
> # Definition of the atoms
> spgroup 62
> spgaxor 2
> spgorig 1
> brvltt 1 # convert conventional cell to prinitive
>
> natrd 3
> natom 12
> typat 1 2 3 # 1 = Pb 2 = Cl  3 = I
>
> acell 9.669 8.2 4.605 Angstrom
> angdeg 90. 90. 90.
> xred
>  0.1240  0.2082  0.25
>  0.0596  0.859   0.25
>  0.8305  0.4703  0.25
> prtvol 3
>
> #Definition of the planewave basis set
> ecut 40.0         # Maximal kinetic energy cut-off, in Hartree
>
> #Definition of the SCF procedure
> nstep 120          # Maximal number of SCF cycles
> diemac  12
>
> ------------ end of input ----------------
>
>
>