From owner-chemistry@ccl.net Sat Nov 3 19:21:00 2012 From: "Sebastian Kozuch kozuchs]~[yahoo.com" To: CCL Subject: CCL: ZPE in non-stationary points Message-Id: <-47835-121103190541-11242-cvuh8jkdr8gukmXmXD4pJg+*+server.ccl.net> X-Original-From: Sebastian Kozuch Content-Type: multipart/alternative; boundary="724907201-1308198894-1351983934=:17657" Date: Sat, 3 Nov 2012 16:05:34 -0700 (PDT) MIME-Version: 1.0 Sent to CCL by: Sebastian Kozuch [kozuchs*yahoo.com] --724907201-1308198894-1351983934=:17657 Content-Type: text/plain; charset=us-ascii 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? Thanks in advance, Sebastian Kozuch --724907201-1308198894-1351983934=:17657 Content-Type: text/html; charset=us-ascii
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?

Thanks in advance,
Sebastian Kozuch

--724907201-1308198894-1351983934=:17657-- From owner-chemistry@ccl.net Sat Nov 3 20:11:00 2012 From: "Jussi Lehtola jussi.lehtola,,helsinki.fi" To: CCL Subject: CCL: ZPE in non-stationary points Message-Id: <-47836-121103201023-2094-9T+6zVdGjObpWNsfrNtXYg-x-server.ccl.net> X-Original-From: Jussi Lehtola Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Date: Sun, 4 Nov 2012 02:10:11 +0200 Mime-Version: 1.0 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" 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 -------------------------------------------------------- Jussi Lehtola, FM Tohtorikoulutettava jussi.lehtola[A]helsinki.fi Fysiikan laitos http://www.helsinki.fi/~jzlehtol Helsingin Yliopisto Työpuhelin: (0)9 191 50 632 --------------------------------------------------------