K-Points for Stepped 111 surface calculation

[hh]

Hi,

The POSCAR of my calculation is simple orthorhombic shape :

Copper stepped surface
2.576134920120
1.000000000000 0.000000000000 0.000000000000
0.000000000000 4.041451931000 -0.816496610641
0.000000000000 1.980295062065 9.801960945129
30
Selective dynamics
Cartesian
0.000000000000 0.000000000000 0.000000000000 F F F
0.500000000000 0.288675129414 0.816496551037 F F F
0.000000000000 0.577350258827 1.632993102074 F F F
0.500000000000 0.866025388241 2.449489593506 T T T
0.000000000000 1.154700517654 3.265986204147 T T T
0.500000000000 1.443375587463 4.082482814789 T T T
0.500000000000 0.866025388241 0.000000000000 F F F
0.000000000000 1.154700517654 0.816496551037 F F F
0.500000000000 1.443375706673 1.632993102074 F F F
0.000000000000 1.732050776482 2.449489593506 T T T
0.500000000000 2.020725965500 3.265986204147 T T T
0.000000000000 2.309400796890 4.082482814789 T T T
0.000000000000 1.732050776482 0.000000000000 F F F
0.500000000000 2.020725727081 0.816496551037 F F F
0.000000000000 2.309401035309 1.632993102074 F F F
0.500000000000 2.598076105118 2.449489593506 T T T
0.000000000000 2.886751413345 3.265986204147 T T T
0.500000000000 3.175426244736 4.082482814789 T T T
0.500000000000 2.598076105118 0.000000000000 F F F
0.000000000000 2.886751174927 0.816496551037 F F F
0.500000000000 3.175426483154 1.632993102074 F F F
0.000000000000 3.464101552963 2.449489593506 T T T
0.500000000000 3.752776861191 3.265986204147 T T T
0.000000000000 4.041451454163 4.082482814789 T T T
0.000000000000 3.464101552963 0.000000000000 F F F
0.500000000000 3.752776861191 0.816496551037 F F F
0.000000000000 4.041451454163 1.632993102074 F F F
0.500000000000 4.330126762390 2.449489593506 T T T
0.000000000000 4.618802070618 3.265986204147 T T T
0.500000000000 4.907476902008 4.082482814789 T T T

and in the OUTCAR :

LATTYP: Found a simple orthorhombic cell.
ALAT = 2.5761349201
B/A-ratio = 4.1231056773
C/A-ratio = 10.0000003451

Lattice vectors:

A1 = ( 2.5761349201, 0.0000000000, 0.0000000000)
A2 = ( 0.0000000000, 10.4113254474, -2.1034054308)
A3 = ( 0.0000000000, 5.1015072615, 25.2511738764)
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
simple orthorhombic supercell.

Subroutine GETGRP returns: Found 4 space group operations
(whereof 2 operations were pure point group operations)
out of a pool of 8 trial point group operations.

The static configuration has the point symmetry C_1h.
The point group associated with its full space group is C_2h.

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

Subroutine DYNSYM returns: Found 4 space group operations
(whereof 2 operations were pure point group operations)
out of a pool of 4 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.
The point group associated with its full space group is C_2h.

Analysis of constrained symmetry for selective dynamics:

Subroutine DYNSYM returns: Found 2 space group operations
(whereof 2 operations were pure point group operations)
out of a pool of 4 trial space group operations
(whereof 2 operations were pure point group operations)
and found also 1 'primitive' translations

The constrained configuration has the point symmetry C_1h.

first of all I think my supercell at least has one mirror plane at the middle
of xy plane but vasp doesn't consider it.
Then if we generate K-points automatically by vasp subroutine it makes kpoints in the quarter of Brillouin zone like this:

Automatically generated mesh
14
Reciprocal lattice
0.00000000000000 0.00000000000000 0.00000000000000 1
0.08333333333333 0.00000000000000 0.00000000000000 2
0.16666666666667 0.00000000000000 0.00000000000000 2
0.25000000000000 0.00000000000000 0.00000000000000 2
0.33333333333333 0.00000000000000 0.00000000000000 2
0.41666666666667 0.00000000000000 0.00000000000000 2
0.50000000000000 0.00000000000000 0.00000000000000 1
0.00000000000000 0.33333333333333 0.00000000000000 2
0.08333333333333 0.33333333333333 0.00000000000000 4
0.16666666666667 0.33333333333333 0.00000000000000 4
0.25000000000000 0.33333333333333 0.00000000000000 4
0.33333333333333 0.33333333333333 0.00000000000000 4
0.41666666666667 0.33333333333333 0.00000000000000 4
0.50000000000000 0.33333333333333 0.00000000000000 2

but I expected to see no symmetry in the Brillouin zone with respect to the point symmetry C_1h.

my questions are :

why does vasp consider the supercell as point symmetry C_1h?

anyway if vasp takes it as point symmetry C_1h why it uses quarter of the Brillouin zone instead of whole Brillouin zone in the xy plane.

I would appreciate for your help and answers to those two questions.

H.Hashemi

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