CCL: ZPE in non-stationary points
- From: Arne Dieckmann <adieckma_+_googlemail.com>
- Subject: CCL: ZPE in non-stationary points
- Date: Sun, 4 Nov 2012 13:25:04 -0800
Sent to CCL by: Arne Dieckmann [adieckma]|[googlemail.com]
Dear Sebastian,
There are ways to do this, but I am not aware of a simple method. You could
employ (ab initio) molecular dynamics and use metadynamics, thermodynamic
integration or something like that to sample phase space and construct a free
energy surface.
Cheers,
Arne
On Nov 4, 2012, at 12:21 PM, "Sebastian Kozuch kozuchs|yahoo.com"
<owner-chemistry#%#ccl.net> wrote:
> Jussi, You have a point here. Let me rephrase my question then:
> Can you calculate the Gibbs energy of a system when you are not at a
minimum or a TS? In other words, is there a simple way to calculate a potential
GIBBS energy surface?
> I'm not a specialist on this, but physically having a stretched molecule
may only mean being at the geometrical limit of a high vibrationally state. In
principle, there should be an equivalent to E+ZPE for each point of the curve of
a reaction (as long as it is permitted by the uncertainty principle). Can
someone share some light on this?
>
> Thanks,
>
> Sebastian
>
>
>
> ________________________________
> From: "Jussi Lehtola jussi.lehtola,,helsinki.fi"
<owner-chemistry- -ccl.net>
> To: "Kozuch, Sebastian " <kozuchs- -yahoo.com>
> Sent: Saturday, November 3, 2012 7:10 PM
> Subject: 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{:}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{:}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{:}helsinki.fi Fysiikan laitos
> http://www.helsinki.fi/~jzlehtol Helsingin Yliopisto
> TyÃpuhelin: (0)9 191 50 632
> --------------------------------------------------------> the strange
characters on the top line to the - - sign. You can also
>
>
> E-mail to subscribers: CHEMISTRY- -ccl.net or use:>
> E-mail to administrators: CHEMISTRY-REQUEST- -ccl.net or use>
>
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>
> <html><body><div style="color:#000;
background-color:#fff; font-family:arial, helvetica,
sans-serif;font-size:10pt"><div><span>Jussi, You have a
point here. Let me rephrase my question then:</span></div><div
style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family:
arial,helvetica,sans-serif; background-color: transparent; font-style:
normal;"><span>Can you calculate the Gibbs energy of a system when
you are not at a minimum or a TS? In other words, is there a simple way to
calculate a potential GIBBS energy surface?</span></div><div
style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family:
arial,helvetica,sans-serif; background-color: transparent; font-style:
normal;"><span>I'm not a specialist on this, but physically having
a stretched molecule may only mean being at the geometrical limit of a high
vibrationally state. In principle, there should be an equivalent to E+ZPE for
each point of the curve of a reaction (as long as it is permitted by
> the uncertainty principle). Can someone share some light on
this?</span></div><div style="color: rgb(0, 0, 0);
font-size: 13.3333px; font-family: arial,helvetica,sans-serif; background-color:
transparent; font-style:
normal;"><br><span></span></div><div
style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family:
arial,helvetica,sans-serif; background-color: transparent; font-style:
normal;"><span>Thanks,<br></span></div><div
style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family:
arial,helvetica,sans-serif; background-color: transparent; font-style:
normal;">Sebastian<br><span></span></div><div
style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family:
arial,helvetica,sans-serif; background-color: transparent; font-style:
normal;"><span></span><br></div><div
style="font-family: arial, helvetica, sans-serif; font-size:
10pt;"> <div style="font-family: times new roman, new york,
times, serif; font-size: 12pt;"> <div dir="ltr">
<font
> face="Arial" size="2"> <hr size="1">
<b><span
style="font-weight:bold;">From:</span></b> "Jussi
Lehtola jussi.lehtola,,helsinki.fi" <owner-chemistry-
-ccl.net><br> <b><span style="font-weight:
bold;">To:</span></b> "Kozuch, Sebastian "
<kozuchs- -yahoo.com> <br> <b><span
style="font-weight: bold;">Sent:</span></b> Saturday,
November 3, 2012 7:10 PM<br> <b><span style="font-weight:
bold;">Subject:</span></b> CCL: ZPE in non-stationary
points<br> </font> </div> <br>
> <br>Sent to CCL by: Jussi Lehtola [jussi.lehtola]^[<a
target="_blank" href="http://helsinki.fi/";>helsinki.fi</a>]<br>On Sat, 3 Nov
2012 16:05:34 -0700 (PDT)<br>"Sebastian Kozuch kozuchs]~[<a
target="_blank" href="http://yahoo.com/";>yahoo.com</a>"
<owner-chemistry{:}ccl.net> wrote:<br>> Dear
all,<br>> Does anyone know of a (simple) method to calculate ZPE
and maybe<br>> Gibbs energies for geometries that are not
stationary points (i.e.<br>> not a stable intermediate or a TS)?
How valid is a typical frequency<br>> calculation for these
geometries?<br><br>Please elaborate on what you
mean.<br><br>Zero point vibrations only make sense in cases where
the potential can<br>be expanded locally as a Taylor series
as<br> V(r) ~ V(r0) +
(r-r0)*d2V/dr2*(r-r0)<br>where d2V/dr2 is the Hessian computed at r0. This
means that you must<br>be in a stationary point, since the first
derivative (gradient) needs
> to<br>vanish.<br><br>Secondly, any stationary point will
not do, since otherwise you will<br>have a saddle point, meaning that
vibrations do not exist in some<br>directions, instead the system is just
unstable: when the system is<br>pushed in this direction, it will not
start to oscillate around the<br>configuration in the stationary point,
instead the perturbation will<br>just start growing.<br><br>To
calculate ZPE you need a bound system. This is not the case even
for<br>all stationary points -- and even less for non-stationary
points.<br>--
<br>--------------------------------------------------------<br>Mr.
Jussi Lehtola, M. Sc. Doctoral
Student<br>jussi.lehtola{:}helsinki.fi
Department of Physics<br>http://www.helsinki.fi/~jzlehtol University of
Helsinki<br>Office phone: +358 9 191 50 632
Finland<br>--------------------------------------------------------<br>Jussi
Lehtola, FM
>
Tohtorikoulutettava<br>jussi.lehtola{:}helsinki.fi
Fysiikan laitos<br><a href="http://www.helsinki.fi/~jzlehtol"; target="_blank">http://www.helsinki.fi/~jzlehtol</a> Helsingin
Yliopisto<br>TyÃpuhelin: (0)9 191 50
632<br>--------------------------------------------------------<br><br><br><br<br<br>the
strange characters on the top line to the - - sign. You can
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</div> </div> </div></body></html>