For a vibration freq. calc.(IBRION=5) POTIM is required to set the displacement size, right? What are the units on POTIM?
For an O2 or an H2 species if I relaxed all the degrees of freedom through POSCAR I should still be getting one real freq. corresponding to the true vibrational mode and the other 5 modes should be 0 I assume?
units of POTIM for a vibrational calc.
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rpnabar
units of POTIM for a vibrational calc.
Last edited by rpnabar on Thu Jun 29, 2006 6:26 pm, edited 1 time in total.
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units of POTIM for a vibrational calc.
--the units of the displacement size is Ã…
--if you do not fix at least one atom, there will also be the degrees of motion of the molecule itself.
--concerning vibrational frequencies of H2: please note that H is treated as a classical atom as well, neglecting the (quantum effect) zero point vibrations. However, H is so light, that one should treat it as a quantum particle. When you do so, the average bond length increases somewhat, since the potential energy surface is not exactly quadratic (anharmonic effect).
--if you do not fix at least one atom, there will also be the degrees of motion of the molecule itself.
--concerning vibrational frequencies of H2: please note that H is treated as a classical atom as well, neglecting the (quantum effect) zero point vibrations. However, H is so light, that one should treat it as a quantum particle. When you do so, the average bond length increases somewhat, since the potential energy surface is not exactly quadratic (anharmonic effect).
Last edited by admin on Fri Jun 30, 2006 12:23 pm, edited 1 time in total.