[molpro-user] ZERO POINT ENERGY

[Peterson, Kirk]

Dear Martin,

within the usual Born-Oppenheimer approximation, the PES is the solution to the electronic Schrödinger equation which is then used as an effective potential for nuclear motion to solve the nuclear motion S.E, i.e., vibrational eigenvalues. If the BO approximation is valid, the usual PES has a very usual interpretation. Somehow defining a whole PES with vibrational motion included makes no sense to me - how do you define vibrational zero-point corrections when the 1st derivatives are non-zero everywhere (except the minimum) ? The harmonic approximation will also presumably be very bad away from the minimum.  Certain approximations can be made along reaction coordinates, but in general I don’t see either the benefit or theoretical rationale for what you suggest.

just my 2 cents,

-Kirk


On Dec 30, 2014, at 8:33 AM, Martin Spenke <martinspenke at yahoo.de<mailto:martinspenke at yahoo.de>> wrote:

Dear Peter,

The well-defined problem is that the transition structure
on an enthalpy surface lacks vibrational energy.
The usual calculated PES is thus physically an unrealistic surface, therefore
the whole PES (namely each point) should be vibrationally
corrected, not only for minimum points but for all.

I guess i have to calculate for every single point on a full optimized PES,
ZPEs and add it to electronic energies afterwards to accomplish the physically realistic one.

Bests
Martin



Peter Reinhardt <Peter.Reinhardt at upmc.fr<mailto:Peter.Reinhardt at upmc.fr>> schrieb am 10:31 Dienstag, 30.Dezember 2014:


Dear Martin,
I'm not sure whether this is a well-defined problem as the zero-point
energy applies to the minimum around which the PES is expanded in a
quadratic form. ZPE concerns the nuclear motion, not the electronic problem.

Yours,
  Peter

Martin Spenke wrote:
> Dear all,
> Is it with molpro possible to calculate PES with the inclusion of zero
> point motion corrections to the energy points of the surface at mrci
> level?If yes, what is the keyword for this ?
> BestsMartin_______________________________________________

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