Graphical representation of phonons at $\Gamma$

Setting the variable LEIGEN = .T. the program produces the files EIGEN.axsf and MODE???.axsf, to be used with the program XCrySDen [5] to visualise phonon vibrations at $\Gamma$. The file EIGEN.axsf contains the eigenvectors of the dynamical matrix. These can be visualised with XCrySden by typing:

xcrysden -axsf EIGEN.axsf

and then ticking in the ``Display'' menu the entry ``Forces''. Atomic displacements for each mode will then be visualised as arrows.

To visualise vibrations dynamically, use the files MODE???.axsf. Typing:

xcrysden -axsf MODE004.axsf

will, for example, visualise mode number 4. The number of cycles of vibrations is two by default, and it can be changed using the variable NCYCLESEIG. The amplitude of the displacement can be altered using the variable EIGSIZE (defualt = 1). The variables NAME? can be used to name the atoms of the primitive cell (default: NAME? = H). The program also writes the EIGEN.xyz files which can be used by the jmol program (http://www.jmol.org) to visualise vibrations. The MODE???.axsf files can also be visualised using VMD (http://www.ks.uiuc.edu/Research/vmd/)