sc-based k-point mesh for bcc compounds

[alexdiazortiz]

Dear All,

I am interested in a series of compounds A_nB_m that are defined on a bcc lattice, e.g., A3B-D03 and A2B2-B32. For that I found very useful and convenient simple cubic kpoint mesh such as

Grid 16x16x16
0
C
0.0625 0 0
0 0.0625 0
0 0 0.0625
0.5 0.5 0.5

that worked well until I tried a low-symmetry structure (a 16-atom base-centered monoclinic cell, see the POSCAR file at the end) for which I got the following error message:

VERY BAD NEWS! internal error in subroutine IBZKPT:
Reciprocal lattice and k-lattice belong to different class of lattices. 12
POSCAR, INCAR and KPOINTS ok, starting setup

the code continues executing as if the error message was not that bad (see the appropriate part of the OUTCAR at the end of this posting).

I have tried the suggestions found in this forum, i.e.,

1. Switching off the symmetry.
2. Using a non-shifted k-point mesh.

but the error remains. Using a Monkhorst-Pack scheme does not produce any error messages but, needless to say, it is not the method I am interested in (unless everything fails;)

I really want to use the sc-based k-point mesh since it provides an unambiguous setting for a series of bcc-based compounds. Have any of you experienced similar problems? How can I get rid of the error message and still use the sc-based k-point mesh? Perhaps, I am doing something totally wrong and if you see it please let me know. Thanks.

Alex




%%% OUTCAR (the structural part that is)

LATTYP: Found a base centered monoclinic cell.
ALAT = 26.1237699707
B/A-ratio = 0.1740776560
C/A-ratio = 0.7177405626
COS(beta) = -0.9566738804

Lattice vectors:

A1 = ( 9.6468413871, -6.4312275914, 6.4312275914)
A2 = ( 6.4312275914, -9.6468413871, 6.4312275914)
A3 = ( -9.6468413871, 9.6468413871, -12.8624551828)
Subroutine PRICEL returns:
Original cell was already a primitive cell.

Analysis of symmetry for initial positions (statically):

Routine SETGRP: Setting up the symmetry group for a
base centered monoclinic supercell.

Subroutine GETGRP returns: Found 2 space group operations
(whereof 2 operations were pure point group operations)
out of a pool of 4 trial point group operations.

The static configuration has the point symmetry C_1h.

Analysis of symmetry for dynamics (positions and initial velocities):

Subroutine DYNSYM returns: Found 2 space group operations
(whereof 2 operations were pure point group operations)
out of a pool of 2 trial space group operations
(whereof 2 operations were pure point group operations)
and found also 1 'primitive' translations

The dynamic configuration has the point symmetry C_1h.

KPOINTS: Grid 16x16x16

Automatic generation of k-mesh.
k-lattice basis in cartesian coordinates

Subroutine IBZKPT returns following result:
===========================================

Found 136 irreducible k-points:

Following reciprocal coordinates:
Coordinates Weight
0.000000 0.062500 0.093750 16.000000
....

%%% POSCAR file
A12B4
-266.0
2.0 -2.0 0.0
1.0 1.0 0.0
1.0 0.0 2.0
12 4
Cartesian
1.0 0.0 0.0 A
1.0 -1.0 0.0 A
2.0 -1.0 0.0 A
2.5 -1.5 0.5 A
2.5 -0.5 0.5 A
2.0 -1.0 1.0 A
2.0 0.0 1.0 A
3.0 -1.0 1.0 A
1.5 -0.5 1.5 A
1.5 0.5 1.5 A
2.5 -1.5 1.5 A
2.5 -0.5 1.5 A
0.0 0.0 0.0 B
1.5 -0.5 0.5 B
1.5 0.5 0.5 B
1.0 0.0 1.0 B

%%% INCAR file
System = A12B4
PREC = Accurate
ISMEAR = 1
SIGMA = 0.1

[Damien]

Hi all,

I have exactly the same problem with one of my simulations, I have also tried the suggestions:

1. Switching off the symmetry.
2. Using a non-shifted k-point mesh.

And the error message still remains,

Any idea please?

Rgds,

Damien

[admin]

the symmetries of real and reciprocal lattice have to match, so you simply cannot use a k-mesh of a cubic lattice if the symmetry of the real space lattice is not cubic as well.