[Pw_forum] Ph.x and force constants calculation questions.

[Zhen Huang]

Dear Users-

This is Alex. I have several beginner questions

1. I wonder if force constants outputs are in the unit of Hartree/bohr^2.

2. For a 2 atoms unit cell, for example, the program (ph.x calcualtion) only
gives the force constants between the atoms but any other, say, second and
third nearest neighbors interactions. Other than increasing the number and
size of unit cell generate non-primitive unit cell, is there a way to obtain
the force constants for atoms beyond the atoms in unit cell?

3. On top of the last question, is there a way to control the cutoff number
of the nearest neighbors.For example,  if I only want to consider upto
fourth nearest neighbor based force constants for a certain material
which perimeter should I study and adjust to gives a promising dispersion
relation based the selected number of force constants from calculation.

Best Regards
-------
Zhen (Alex) Huang
Ph.D. Student
Nanoscale Transport Research Group
Laboratory for Computational Methods in Emerging Technologies
Cooling Technologies Research Center
School of Mechanical Engineering
Purdue University
Tel: 765 237 9733
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