ABINIT Discussion Forums

Hello community

I have problems concerning fixing atoms in response function calculation.
I have tried to fix the atoms with natfix and iatfix in an RF calculations but it failed. Apparently, the natfix and iatfix options only fix atoms during structur optimization.

My needs are to fix all atoms except two and make a phonon calculation. The two free atoms are free to move around in the potential of the other fixed atoms. The fixed atoms are not allowed to move or vibrate. So that, Abinit must only calculate the perturbations of the free atoms.

Similar to moving atoms in a outer constant potential.


Does someone have some suggestions or suitable input variables ?

Thanks in advance!

Chris

I just thinking about changing the mass to a high value should fix the atoms and stop the vibration. But I am not sure wether in RF case the atoms will displaced during calculation and so, the potential will change. Is this correct ?

Chris

Hi Chris

During a RF calculation, the atoms are not displaced.The second derivative of the total energy is calculated analytically. It's not like a frozen phonon calculation where you have to displace an atom and calculate the forces that act on each atom relative to this displacement.

Boris