computed multigrid residual is greater than the required accuracy

[Dipankar Saha]

WARNING                                                             
# The computed multigrid residual is greater than the required accuracy.     
# Computed residual :   1.20533e-11                                         
# Required accuracy :   1.00000e-12                                           

............ What does this warning message signify???                                 

[kstokbro]

This error is related to the accuracy of the multigrid solver. 1e-11 is still a very small number, thus, I think it is safe to continue. However, please send your inputfile to [email protected], with an explanation, such that we can check the problem.

[Dipankar Saha]

Okay... I'm continuing with it.... / Besides, I will mail the *.py file with due explanations....to [email protected]
Thanks 

[tara]

 The computed multigrid residual is greater than the required accuracy.     
# Computed residual :   1.20533e33                                         
# Required accuracy :   1.00000e-12
                     
I have used multigrid with periodic boundary contions in A and B directions in my structure that is gated .

what could be the reason for such huge difference.??

[Anders Blom]

Please tell us how we are supposed to help you when we have zero idea of what calculation you are performing, what input parameters are used, etc?

[tara]

sorry ,i forgot to mention the calculation and input parameters.

I am using DFT calculation,with poisson solver setting as multigrid.I have given boundary conditions as periodic in A and B directions.My structure is p-i-n gated transistor. For doping i have replaced some  Si atoms with boron atoms for p-type doping and with phosphorous atoms for n -type.

i am getting this warning repeatedly

The computed multigrid residual is greater than the required accuracy.     
# Computed residual :   1.20533e33                                         
# Required accuracy :   1.00000e-12

why am i getting such huge difference??

[Anders Blom]

Attach the whole script, otherwise we can't reproduce it.

[tara]

i am atttaching my script here.

please help as to why i am getting huge difference in required and obtained values

[Anders Blom]

Your gate is outside the simulation cell and therefore not included in the calculation. Moreover it looks like you attempt to have periodic boundary conditions in the Y direction while at the same time having a gate there, this will not work. If you are using gates, you need Dirichlet on the gate (cf. http://quantumwise.com/forum/index.php?topic=1597.0).

Also, you will need to passivate all the Si surface atoms to eliminate dangling bonds (this is not related to the multigrid residual though).