The ABINIT Users Mailing List ( CLOSED )

["Corsin Battaglia" <corsin.battaglia@freesurf.ch>]

Dear Matthieu, dear Abinit users

First of all, thanks for your mail. I increased my nstep value and added the
prtvol command, so my bandstructure looks quite O.K. now.
What I do not understand at all is the following: According to the manuel
entry for the iscf command, iscf=-2 results in a non-self consistent
calculation. Makes sense to me, since eigenvalues are computed at fixed self
consistent potential, which  was determined in a previous scf-run (prtden
after scf, getden for bandstructure calculation). But then why did I have to
increase nstep? And why abinit has to converge the eigenvalues? In my
opinion, it is sufficient to put the self-consistent potential into the
Hamiltonian and to diagonalize it.

Well, maybe it is more complicated then I thought it is?
Thanks for your answer.

Corsin

P.S.: I wrote a little Igor Pro procedure, which automatically reads in the
abinit output file and plots the bandstructure. Just in case, somebody is
interested.



----- Original Message -----
From: <verstraete@pcpm.ucl.ac.be>
To: <forum@abinit.org>
Sent: Monday, February 02, 2004 11:50 AM
Subject: Re: [abinit-forum] fuzzy bandstructure


>
>
> Hello Corsin,
>
> The (stupid) problem is that by default abinit only prints 50 kpoints. The
> calculation didn't have enough nsteps to converge all the points (hence
> the fuzziness), but then it didn't print out the data it calculated. Set
> prtvol 10 to print out everything, and increase nstep (for dtset 2 it is
> the default of 1 - you only specified nstep1 not nstep2).
>
> We should print a separate file with the eigenvalues in good formats
> (xmgr, with a linear coordinate along the band structure), but someone has
> to sit down and code it in abinit - not hard. Volunteers?
>
> Matthieu
>
>
> On Sun, 1 Feb 2004, Corsin Battaglia wrote:
>
> > Dear abinit users
> >
> > I am trying to calculate the bandstructure for the metallic compound
NbS2.
> > In a first step, I computed the total energy. I used the Hartwigsen-Goed
ecker-Hutter pseudopotentials for Nb and S. For Nb, I used the one, which
contains semicore states as well (I read somewhere that semicore states are
necessary in an electronegative environment).
> > During the scf-cycle, there seem to be no convergence problems.
> >
> >      iter   Etot(hartree)      deltaE(h)  residm     vres2    diffor
maxfor
> >
> >  ETOT 14  -154.22694726148    -3.875E-11 1.106E-04 8.090E-09 1.155E-06
2.924E-02
> >  ETOT 15  -154.22694726148    -2.394E-12 1.110E-04 8.903E-10 2.442E-07
2.925E-02
> >  ETOT 16  -154.22694726148    -9.612E-13 4.247E-05 5.884E-10 3.020E-07
2.925E-02
> >  ETOT 17  -154.22694726148    -4.440E-13 3.888E-05 6.675E-12 1.490E-07
2.925E-02
> >
> > The Fermi energy converges as well
> >
> > 11792: newocc : new Fermi energy is       0.247380 , with nelect=
50.000000
> > 12728: newocc : new Fermi energy is       0.247382 , with nelect=
50.000000
> > 13664: newocc : new Fermi energy is       0.247381 , with nelect=
50.000000
> > 14600: newocc : new Fermi energy is       0.247381 , with nelect=
50.000000
> > 15536: newocc : new Fermi energy is       0.247381 , with nelect=
50.000000
> > 16472: newocc : new Fermi energy is       0.247381 , with nelect=
50.000000
> > 17408: newocc : new Fermi energy is       0.247381 , with nelect=
50.000000
> >
> > No warnings or errors up to this point.
> > In a second step, I calculated the bandstructure. When I plot the
bandstructure, it looks very fuzzy, although the number of k-points was
quite dense (50 k-points between Gamma and M).
> >
> >
> > For every k-point, abinit writes the following warning into the log file
> >
> > 17759: vtowfk: WARNING -
> > 17760-  Wavefunctions not converged for nnsclo,ikpt=    1    1 max
resid=  1.22992E+00
> >
> > Another problem is that abinit stops after 50 k-points, although I
intended to compute 125 k-points.
> >
> > I have no clue, what I am doing wrong.
> > Thanks in advance for your help
> >
> > Corsin
> >
> >
> >
> > Here's are the files I used.
> >
> > NbS2.files
> >
> > NbS2.in
> > NbS2.out
> > NbS2i
> > NbS2o
> > NbS2
> > ../../Pseudopotentials/41nb.13.hgh
> > ../../Pseudopotentials/16s.6.hgh
> >
> >
> > NbS2.in
> >
> > # 2H-NbS2 : computation of the total energy and bandstructure
> >
> > #Definition of the unit cell
> > acell   3.31   3.31    11.89 angstrom
> > #rprim  0.866 -0.500   0.000     # It is better to define
> > #       0.000  1.000   0.000     # the primitive vectors
> > #       0.000  0.000   1.000     # using rprim
> > angdeg 90 90 120
> >
> > #Definition of the atom types
> > ntypat 2          # There are two type of atoms
> > znucl 41 16       # 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
> > natom 6           # There are six atoms
> > natrd 2           # Reads two atoms
> > typat 1 2         # type 1 is Nb, type 2 is S
> > xred              # This keyword indicate that the location of the atoms
> >                   # will follow, one triplet of number for each atom
> >    0.0  0.0  1/4  # Triplet giving the REDUCED coordinate of atom 1.
> >    1/3  2/3  1/8  # Triplet giving the REDUCED coordinate of atom 2.
> >                   # Note the use of fractions (remember the limited
> >                   # interpreter capabilities of ABINIT)
> > spgroup 194
> >
> > #Definition of the occupation numbers
> > occopt 4
> > tsmear 0.01
> >
> > #Read psp
> > npsp 2            # Read 2 psp files
> > ixc 1             # Nb is of type ixc 1. S is of type ixc 1.
> >                   # LDA. Nb contains semicores.
> >
> >
> > #Definition of the planewave basis set
> > ecut 10.0         # Maximal kinetic energy cut-off, in Hartree
> >
> > ndtset 2
> >
> > #Dataset 1: SCF GS calculation
> >
> > #Definition of the k-point grid
> > kptopt1 1         # Option for the automatic generation of k points,
taking
> >                   # into account the symmetry
> > ngkpt1 8 8 4      # This is the grid based on the primitive vectors
> >                   # of the reciprocal space
> >
> >
> > #Definition of the SCF procedure
> > iscf1 3           # SCF cycle, CG based on the minim of the energy
> > nstep1 250        # Maximal number of SCF cycles
> > toldfe1 1.0d-12    # Will stop when, twice in a row, the difference
> >                   # between two consecutive evaluations of total energy
> >                   # differ by less than toldfe (in Hartree)
> > #diemac 12.0      # For metals, we use the default 10^6.
> > nband1 35         # nband=nb of electrons in unit cell/2+(20% for
metals)
> >                   # more bands are needed with semicore states
> > prtden1 1         # Print the density for use by dataset 2
> >
> > #Dataset 2: band structure
> >
> > iscf2 -2          # Non-SCF calculation
> > getden2 -1
> > kptopt2 -4        # Bandstructure with 4 lines
> > nband2 35         # 35 bands
> > ndivk2 50 25 50 10
> > kptbounds2      0.0  0.0  0.0 # Gamma point
> >                 0.5  0.0  0.0 # M point
> >                 2/3  2/3  0.0 # K point
> >                 0.0  0.0  0.0 # Gamma point
> >                 0.0  0.0  0.5 # A point
> > tolwfr2 1.0d-12   # Only admitted convergence criterion for non-SCF
calculations
> > enunit2 1         # Output the eigenvalues in eV
> >
> >
>
> --
> ===================================================================
> Matthieu Verstraete               mailto:verstraete@pcpm.ucl.ac.be
> PCPM, Boltzmann, pl. Croix du Sud, 1            tel: 010/ 47 33 59
> B-1348 Louvain-la-Neuve  Belgium                fax: 010/ 47 34 52