PM is used for obtaining DISP file involving plus and minus displacements. In this tag, only the plus and minus displacements which are symmetrically different are output. Sometimes phonon frequency is not well calculated even if equilibrium structure is highly optimized. This is often because the structure in which an atom is displaced in one direction is symmetrically different from that in which the atom is displaced in the opposite direction. The plus and minus displacements are useful, when you want to counteract the finite displacement errors.
	PM = .TRUE.

togo 2009-02-12
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