CCL:G: clatharte (calc of deltah and deltag; Should I use readisotope option)



 Sent to CCL by: [david.anick{:}rcn.com]
 Dear Raj,
 This is not exactly what you asked, but is relevant to your study.  It is not as
 widely known as I'd like it to be, that the specific topological configuration
 of the
 clathrate cell matters substantially to E0 and G.  In studies like yours it is
 important to make a deliberate choice of how the H-bonds are ordered in the
 cage (e.g. to choose a low energy configuration), rather than just come up with
 any arrangement that satisfies the ice rules.  For what I believe is the most up
 to
 date study of 5^12 (H2O)20 cages, see
 D. Anick, J. Chem. Phys. 132, 164311 (2010).
 As to extracting thermodynamic information at other temperatures, the
 Gaussian jobname.out file containing the frequencies and normal modes should
 be enough.  There is no need to re-run a Gaussian calculation for each new
 temperature.  Dr. Karl Irikura's perl script "thermo.pl", based on the
 RRHO model,
 is commonly used for this purpose.
 Peace,
 David Anick
 ---- Original message ----
 >Date: Sat, 2 Oct 2010 01:31:34 -0400
 >From: owner-chemistry+david.anick==rcn.com,,ccl.net (on behalf of "Raj
 Thakur Veer meandme_meandme2003%x%yahoo.com" <owner-
 chemistry,,ccl.net>)
 >Subject: CCL:G: clatharte (calc of deltah and deltag; Should I use
 readisotope
 option)
 >To: "Anick, David " <david.anick,,rcn.com>
 >
 >
 >Sent to CCL by: "Raj  Thakur Veer"
 [meandme_meandme2003!=!yahoo.com]
 >Dear CCLers, In a system of clathrate having an entraped guest-gas atom (20
 water molecules and 1 noble gas atom in its cage), is this the way to calculate
 deltaH and deltaG from Gaussian 09 Therochemistry output.
 >deltaH= [Eo+Hcorr (of whole system)] - [Eo+Hcorr (of 20 water molec) +
 Eo+Hcorr (of guest atom)]
 >
 >Similarly deltaG would be calculated as;
 >
 >deltaG= [Eo+Gcorr (of whole system)] - [Eo+Gcorr (of 20 waer molec) +
 Eo+Gcorr (of guest atom)]
 >
 >Secondly, in order to calculate thermochemical data at a different
 temperature
 then default (298.15 k and 1 atm) in gaussian 09, should I use the readisotope
 option in gaussian 09 to use my exp. temp and pressure or I can just use
 freqchk command to extract data at different temp and pressures from
 checkpoint file I have saved from calculations which originally were done at
 default gaussian temp of 298k and 1 atm.for instance, if I want to extract data
 at 0k, 100k and 150k (or else) and 1000 atm. should I use freqchk command in
 gaussian to extract data  at this specific temp and pressure or should i rerun
 gaussian calc and use readisotope option to specify my exp. temp and pressure.
 BUt again, should i have to rerun new calc for every temp. and pressure value. I
 appreciate your help.
 >
 >~Titan>
 >