# [Wannier] problem for hexagonal cell

Hongwei Wang whw1985 at mail.ustc.edu.cn
Sun Apr 29 18:55:20 CEST 2012

```Dear Wannier90 users and developers：

I get an error from wannier90 that I don't know how to fix. I am attempting to do a calculation for hexagonal
cell.

Lattice Vectors (Ang)
a_1     5.151418  -2.974197   0.000000
a_2     0.000000   5.948357   0.000000
a_3     0.000000   0.000000  11.694322

Unit Cell Volume:     358.34296  (Ang^3)

Reciprocal-Space Vectors (Ang^-1)
b_1     1.219700   0.000000   0.000000
b_2     0.609854   1.056289   0.000000
b_3     0.000000   0.000000   0.537285

I got an error message after executing the command wannier 90 -pp seedname.

B1 condition is not satisfied: Adding another shell
Exiting.......
kmesh_get_bvector: Not enough bvectors found
+----------------------------------------------------------------------------+
|                    Distance to Nearest-Neighbour Shells                    |
|                    ------------------------------------                    |
|          Shell             Distance (Ang^-1)          Multiplicity         |
|          -----             -----------------          ------------         |
|             1                   0.134321                      2            |
|             2                   0.152463                      6            |
|             3                   0.203192                     12            |
|             4                   0.264073                      6            |
|             5                   0.268643                      2            |
.
.
.
+----------------------------------------------------------------------------+
I set the parameter kmesh_tol = 0.018143 and executed the command "wannier 90 -pp seedname"
again, however, I got another erro message:

Exiting.......
kmesh_get_bvector: Not enough bvectors found

+----------------------------------------------------------------------------+
|                    Distance to Nearest-Neighbour Shells                    |
|                    ------------------------------------                    |
|          Shell             Distance (Ang^-1)          Multiplicity         |
|          -----             -----------------          ------------         |
|             1                   0.134321                      8            |
|             2                   0.203192                     12            |
|             3                   0.268643                      8            |
|             4                   0.308891                     30            |
|             5                   0.333199                     12            |
.
.
.
+----------------------------------------------------------------------------+

The smallest shell (a star of 6 vectors) is good for cubic crystal. Two shells
(star of 4 vecors and star of 2 vector) will be a enough to describe a gradient
in tetragon cell. To satisfy B1 in a simple orthorhombic cell( a/=b/=c angles=90),
it need 3 kpoint shells, each with 2 kpoints (6 total). It has too many vecors in
the second shell to find enough bvectors for hexagonal cell, but if I don't consider
the second shell,the B1 condition will not be satisfied. I wonder if someone can give
me some suggestions to fix this problem. Thanks for any help.

Best regards

Hongwei Wang

```