query regarding mesh cutoff

[Val]

sir,
 
while trying to run a problem with a mesh cut off of 100rydberg,pseudopotential error message was generated.

1.how is the grid mesh cut off determined for any simulation?is it determined by any material parameters?

2.can the mesh cut off be different for the source,drain and the channel regions?i.e if source and drain are given a mesh cut off of 50Ry,and the channel is given 75Ry will it run without any error?Or is the mesh cut off uniform throughout?How is it to be given and determined?

[Anders Blom]

We would need to see input and detailed output (exact error messages) to determine what is at play here.

1) The grid mesh cut-off (if we are talking the 3D grids for the real-space representation of the potentials and density used for the Poisson equation) are specified by the user as an input parameter. As you can see from the manual, the value is given as an equivalent energy. The default is 75 Hartree which corresponds to [tex]\Delta x=0.136[/tex] Å.

2) That is not recommended.