[Pw_forum] NEB input cell parameters

Mitul Mundra mitulm at iitk.ac.in
Thu Feb 6 07:36:18 CET 2014


I need to do NEB calculations for my system. My system consists of Si 2*2*2
supercell with some Li impurities. Prior to NEB, I am doing a vc-relax
calculation to get the minimum energy states for the first and the last
images of the NEB. For the vc-relax, I set *ibrav = 1* for the symmetric
cubic system. In the results obtained from vc-relax calculation, the cubic
symmetry of the system is lost and I get the following call parameters for
the initial and final state in the output file.

CELL_PARAMETERS (alat= 20.51108588)
   1.011059885  -0.002882944  -0.000008465
  -0.002882944   1.011059885   0.000008465
  -0.000008492   0.000008492   1.007297719

CELL_PARAMETERS (alat= 20.51108588)
   1.004932042   0.000000442  -0.000000442
   0.000000442   1.004688370   0.000104290
  -0.000000442   0.000104290   1.004688370

Now, I am confused about my input file for the NEB. I can not just directly
change the lattice constant by taking the cube root of the new volume
obtained. I tried to set* ibrav = 0* and give the cell parameters obtained
but I can only enter them once (correct me if I am wrong) and thus, can not
incorporate both the set of cell parameters. I would be extremely thankful
if anyone could suggest me a way to tackle this difficulty.

Mitul Mundra
Final year Dual Degree Student
Department of Chemical Engineering
IIT Kanpur
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