On Thu, 31 Jul 2008, Paolo Giannozzi wrote: PG> PG> > [...] I displaced atoms in the cell according PG> > to the eigen-displacements shown above,and got a cubic cell containg 8 PG> > atoms. But I found the energy rised with the increase of atom PG> > displacements, which was totally contrary to what I expected. PG> PG> have you tried the same operation on a simpler system, such as e.g. PG> GaAs? You should get the phonon frequencies. If you don't, you PG> may have made a mistake
... not to mention that several of the pseudopotentials from the vanderbilt library have problems with getting phonons right. not sure whether this originates from the definition of the potentials or the individual parameters chosen. i've seen this in several vanderbilt pseudopotential that i created: they worked fine for all problems that i was using them (MD, geometry optimization), but when others used them for calculating phonons, they turned out to be disastrous. cheers, axel. PG> PG> Paolo PG> -- ======================================================================= Axel Kohlmeyer akohlmey at cmm.chem.upenn.edu http://www.cmm.upenn.edu Center for Molecular Modeling -- University of Pennsylvania Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323 tel: 1-215-898-1582, fax: 1-215-573-6233, office-tel: 1-215-898-5425 ======================================================================= If you make something idiot-proof, the universe creates a better idiot.
