Calculation of optimized surface structure

[abhishek_sharmacct]

Hello Everyone
I want to  calculate optimized structure of the surface[110] of W.
I have attached my file. By running it I am getting following error:

Traceback (most recent call last):
  File "c:/docume~1/cct/locals~1/temp/tmpyc5cps.nl", line 98, in ?
    scf=kohnsham_method.apply(my_cell)
ATKError: solveHermitianGeneralizedEigenProblem : Failed to diagonalize matrix!
Terminated Abnormally

Please help me to solve it.
I want to ask
-Is Vacuum extension of my structure is wrong or there is any other problem with my unit cell or with k point specification.
-What is the function of solveHermitianGeneralizedEigenProblem and why it fails to diagonalize matrix for my structure.

Thanks in advance

[zh]

The setup in your script file indicates that an atomic layer of W (110) surface is calculated. In the primitive unit cell of W(110) surface, each atomic layer contains only two atoms. But there are fours atoms in your script file, and so some of them will be overlapped due to the periodicity.

unit_cell=[[1.414*a, 0.0, 0.0],
         [0.0,    a,   0.0],
         [0.0,    0.0, b]]*Angstrom
here b stands for the thickness of vacuum, 1.414*a and a are the lattice constants of W(110) surface in the xy plane.  Maybe  10 is enough for b.

my_cell=PeriodicAtomConfiguration(
      super_cell_vectors=unit_cell,
      elements=2*[Tungsten],
      fractional_coordinates=[(0.0,0.5,0.0),(0.5,0.0,0.0)]
      )