another question in relation to the dynamical matrix method

[chwang45]

I wan to make sure that my understanding is correct.

I looked through the perl script, which makes the dynamical matrix and concluded that I can use different displacements for different atoms in DISPLACECAR. Right now, the script which generates DISPLACECAR can generate DISPLACECAR with the same displacement for all particles (atoms or ions). I hope that there is nothing wrong in using different displacements for different particles.

[graeme]

Blas can you weigh in here. I was going to say that a single displacement was needed for the dymmatrix.pl script, but looking it now, I agree with chwang that although a single displacement is entered -- it is never used. Is this right? Can't we just eliminate that input paramter?

[buber]

It's been a while, but it does look like the <displacement> argument isn't used. It must be that at one point I used it to calculate the actual force constants, rather than just the force difference, which is what it seems it is spitting out right now. So, I'm a little confused as to when it actually divides by the displacement. In an older version of that script, I did use the <displacement> to divide the force difference.

The displacement is currently read directly from the DISPLACECAR itself, so I don't believe that argument is needed at all any more.