CCL: ZPE in non-stationary points

 Sent to CCL by: Jussi Lehtola [jussi.lehtola]^[helsinki.fi]
 On Sat, 3 Nov 2012 16:05:34 -0700 (PDT)
 "Sebastian Kozuch kozuchs]~[yahoo.com"
 <owner-chemistry[A]ccl.net> wrote:
 > Dear all,
 > Does anyone know of a (simple) method to calculate ZPE and maybe
 > Gibbs energies for geometries that are not stationary points (i.e.
 > not a stable intermediate or a TS)? How valid is a typical frequency
 > calculation for these geometries?
 Please elaborate on what you mean.
 Zero point vibrations only make sense in cases where the potential can
 be expanded locally as a Taylor series as
 	V(r) ~ V(r0) + (r-r0)*d2V/dr2*(r-r0)
 where d2V/dr2 is the Hessian computed at r0. This means that you must
 be in a stationary point, since the first derivative (gradient) needs to
 vanish.
 Secondly, any stationary point will not do, since otherwise you will
 have a saddle point, meaning that vibrations do not exist in some
 directions, instead the system is just unstable: when the system is
 pushed in this direction, it will not start to oscillate around the
 configuration in the stationary point, instead the perturbation will
 just start growing.
 To calculate ZPE you need a bound system. This is not the case even for
 all stationary points -- and even less for non-stationary points.
 --
 --------------------------------------------------------
 Mr. Jussi Lehtola, M. Sc.         Doctoral Student
 jussi.lehtola[A]helsinki.fi         Department of Physics
 http://www.helsinki.fi/~jzlehtol  University of Helsinki
 Office phone: +358 9 191 50 632   Finland
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 Jussi Lehtola, FM                 Tohtorikoulutettava
 jussi.lehtola[A]helsinki.fi         Fysiikan laitos
 http://www.helsinki.fi/~jzlehtol  Helsingin Yliopisto
 TyÃpuhelin: (0)9 191 50 632
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