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[Stephen Derenzo <sederenzo@lbl.gov>]

Gian-Marco

Thanks for your reply. Obviously I am doing something wrong, since spgaxor 4 is the thing I first tried. But when I try it using abinis 4.4.3, I get

 abinit : ERROR -

  operat : The number of atoms obtained from symmetries,   8

  is lower than the input number of atoms, natom=     20

  This is not allowed.

  Action : modify natom or the symmetry data in the input file.

My entire input file is:

# Crystalline Bi Pb O2 Cl

# ICSD 31860  B m m b (63)

# Computation of the band structure.

# First, a SCF density computation, then a non-SCF band structure calculation.

ndtset 2

chkprim 0

#Dataset 1 : usual self-consistent calculation

kptopt1 1          # Option for the automatic generation of k points,

                   # taking into account the symmetry

nshiftk1 4

shiftk1  0.5 0.5 0.5  # These shifts will be the same for all grids

         0.5 0.0 0.0

         0.0 0.5 0.0

         0.0 0.0 0.5

ngkpt1  3 3 3 

nband1   60

prtden1  1         # Print the density, for use by dataset 2

prtdos1 3          # print s, p, d, f DOS for individual atoms

natsph 4           # number of atoms for DOS

iatsph 1 2 3 4     # atom indices for DOS

ratsph 1.2 angstrom  # radius for all DOS

toldfe1  1.0d-6

#Dataset 2 : the band structure

iscf2    -2

getden2  -1

kptopt2  -6

ndivk2   5 5 5 5 5 5        # 37 k points

kptbounds2  0    0     0    # Gamma point

            1    0     0    # Y point

            0    0     1/2  # Z point

            1/2  1/2   1/2  # R point

            1/2  1/2   0    # S point

            1     0    1/2  # T point

            0     0    0    # Gamma point

nband2   60

tolwfr2  1.0d-12

enunit2  1             # Will output the eigenenergies in eV

# Definition of the unit cell:

acell 5.627 5.575 12.425 angstrom   # a, b, c

angdeg 90 90 90       # alpha, beta, gamma

# Definition of the atom types

ntypat  4         # There are 4 types of atoms

znucl 82 83 17 8  # 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 63    # determine conventional unit cell

spgaxor 4    # value from the ABINIT space groups table for B m m b

spgorig 1    # value from the ABINIT space groups table for B m m b

brvltt -1      # generate primitive unit cell

natrd 4         # number of atoms in the asymmetric cell

natom 20         # number of atoms in the primitive unit cell

typat  1 2 3 4   # Pb Bi Cl O

xred      # Reduced coordinates of atoms

0           0.25        0.385    

0           0.25        0.09     

0           0.25        0.75     

0.25        0           0        

prtvol 3

# mkmem 0   

# mffmem 0

#Definition of the planewave basis set

ecut 60.0         # Maximal kinetic energy cut-off, in Hartree

#Definition of the SCF procedure

nstep 100          # Maximal number of SCF cycles

diemac 12.0       # Although this is not mandatory, it is worth to

                  # precondition the SCF cycle. The model dielectric

                  # function used as the standard preconditioner

                  # is described in the "dielng" input variable section.

                  # Here, we follow the prescription for bulk silicon.

On Nov 16, 2005, at 12:34 PM, Gian-Marco Rignanese wrote:

Dear Steven,

I apologize for my partly incorrect answer... Following Razvan suggestion (who is THE expert since he coded the symmetries), I checked that with "spgaxor 4" (as you had done in the beginning) everything works fine.

Dear Katalin,

for your information, the number of equivalent positions for the various atoms is different. From the table, we can see that Pb, Bi, and Cl occupy 4c sites (4 equivalent positions) while O is on a 8e Wyckoff site (8 equivalent positions). Hence, despite the number of independent atoms is 4, the unit cell contains 4+4+4+8=20 atoms (which is indeed a multiple of 5).

Best regards,

Gian-Marco.

_______________

Stephen E. Derenzo

Senior Scientist

Lawrence Berkeley National Laboratory

Mail Stop 55-121

Berkeley, CA 94720

(510) 486-4097 (fax 486-4768)

sederenzo@lbl.gov

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