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[SOLVED] Pressure difference in optimization and band struc

Posted: Wed Feb 24, 2010 11:51 am
by ilukacevic
Dear colleagues,

I'm trying to calculate the band structure at some specific pressure of VN.

First I optimized the structure at that specific pressure and then copied the relaxed structure in the band structure calculation. However, the pressure abinit gives in the end of the 1st dataset of the band structure calc. (3.3 GPa) is different from the specified one (10 GPa).

I'm using the same parameters in both calculations as can be seen from the input files I attached. Could someone help me and explain why this happens?

Thank you all in advance!

Yours,
Igor Lukacevic

Re: Pressure difference in optimization and band structure calcu

Posted: Wed Feb 24, 2010 1:44 pm
by mverstra
Need output too. Your input looks ok, but it is suspicious that it is just 1/3 of the desired pressure...

check how well converged it is, of course...

Re: Pressure difference in optimization and band structure calcu

Posted: Thu Feb 25, 2010 4:51 pm
by ilukacevic
Dear prof. Verstraete,

I'm sending the output files. I hope that they will reveal something.

I've checked the convergence of the pressure while I was checking the convergence of the relaxation at the zero pressure. Used parameters converged the pressure very close to 0 GPa (10^(-7) GPa). When I was optimizing the lattice parameter at different pressures, abinit gave out the exact values of 10, 20,... GPa. I took as a sign of good convergence.

Hope this will help You to help me.

Yours,
Igor Lukacevic

Re: Pressure difference in optimization and band structure calcu

Posted: Fri Feb 26, 2010 12:46 am
by mverstra
You should keep the same ecutsm after the relaxation: it affects the PW set which is used, and determines the convergence to a certain extent (effectively increases ecut for the relaxation run). Same thing for dilatmx, which is not echoed in your outputs... In this case it changes the fft grid quite a bit (your dilatmx is quite high):

ngfft 32 32 32
ngfft 40 40 40

In practice, this means your relaxation was done with a higher real ecut. The pressure is very sensitive to the ecut and ecutsm/dilatmx, but you can see that the etotal is also very different between the two files.

Matthieu

Re: Pressure difference in optimization and band structure calcu

Posted: Fri Feb 26, 2010 11:03 am
by ilukacevic
Oh, yes! Thank You a lot for reminding me about the consistency.

I'll be back with the results.

Yours,
Igor Lukacevic

Re: Pressure difference in optimization and band structure calcu

Posted: Fri Feb 26, 2010 10:25 pm
by ilukacevic
Dear prof. Verstraete,

Your corrections proved to be essential. After turning on ecutsm and dilatmx, pressures in the band structure calc. were the same as in the relaxation calc.

Thank You again!

Yours,
Igor Lukacevic