From owner-chemistry@ccl.net Sun Jun 6 01:19:01 2010 From: "Kalju Kahn kalju{=}chem.ucsb.edu" To: CCL Subject: CCL:G: Infrared calculation at different temperature Message-Id: <-42063-100606004644-31891-9J/w6p7JMO8ejdcqRLj7Hg||server.ccl.net> X-Original-From: "Kalju Kahn" Content-Transfer-Encoding: 8bit Content-Type: text/plain;charset=iso-8859-1 Date: Sat, 5 Jun 2010 21:46:33 -0700 MIME-Version: 1.0 Sent to CCL by: "Kalju Kahn" [kalju ~~ chem.ucsb.edu] Lalitha, As previous replies have said, calculated frequencies are temperature independent. To see why this is so, recall that harmonic frequencies are calculated based on the equilibrium geometry, and geometric second derivatives of structural displacements. As long as the molecular PES is temperature-independent (there is no temperature in the Schrodinger equation), derivatives are temperature independent. Fundamental frequencies are obtained from harmonic frequencies and anharmonicity corrections. The latter include cubic and quartic energy derivatives, and small contributions from rotational constants at the equilibrium geometry. Again, all these are usually taken as temperature-independent. Vibrational intensities depend on dipole moment derivatives with respect to nuclear displacement. Dipole moments of individual molecules (or geometries) in the gas phase are temperature-independent, so infrared intensities are also temperature-independent. Raman intensities depend on polarizability derivatives with respect to nuclear displacement. Polarizabilities in the gas phase are temperature-independent, so Raman intensities are also temperature-independent. Does this mean that the observed IR spectra are temperature-independent? Almost, but not quite. First, recall that at normal temperatures, most molecules reside in the vibrational ground state, and we usually see v=0 -> v=1 transitions. The v=1 -> v=2 transitions are also allowed, but the Boltzmann probability of the v=1 state is negligible at the room temperature. But when you heat your molecule up to 2000K, you populate this state, and can observe the v=1 -> v=2 transitions. These are sometimes called hot bands. Note that you do not need to run a Gaussian calculation at 2000 K to predict the position of the hot band; you just need to perform an anharmonic calculation and figure out vibrational energy levels. Second, recall that molecules also rotate, and the population of rotational states changes with temperature. If you use a low-resolution IR instrument, you cannot resolve the rotational fine structure, but you see the peak maximum shifting to lower frequencies because you starting point is a higher rotational level in the v=0 state. To study this effect, you would need to calculate rotational states, and ro-vibrational coupling, I think. Last, IR spectra in liquids and solids depends on temperature because the structure of many liquids or solids (e.g. liquid crystals) is temperature-dependent. But this is a domain of molecular simulations, not quantum mechanics. Hope this clarified the confusion, Kalju > > Sent to CCL by: "Lalitha Selvam" [lselvam ~~ swin.edu.au] > Hi, > > I would like to calculate infrared and raman at different temperatures. I > found > keyword from gaussian manual and calculated the frequencies at 10K. > however > when i compare the frequencies of default temperature with 10k, it is > same. > > The keywords used : > > #P B3LYP/6-31G* freq=raman Temperature=10.0 SCF=(Tight)IOP(6/7=3)IOP(6 > /79=1) > > I am confused with what went wrong. I would greatly appreciate if anyone > can > help on this. > > Thanks > Lalitha > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dr. Kalju Kahn Department of Chemistry and Biochemistry UC Santa Barbara, CA 93106 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dr. Kalju Kahn Department of Chemistry and Biochemistry UC Santa Barbara, CA 93106 From owner-chemistry@ccl.net Sun Jun 6 10:25:00 2010 From: "Alavi, Saman Saman.Alavi===nrc-cnrc.gc.ca" To: CCL Subject: CCL: Nanoparticles Message-Id: <-42064-100606093941-10814-wYvFjSzW+By7szwHaIgRWg|-|server.ccl.net> X-Original-From: "Alavi, Saman" Content-Language: en-CA Content-Type: multipart/alternative; boundary="_000_001A8CD833A9894A8AED786976F900240F09C435NRCCENMB1nrcca_" Date: Sun, 6 Jun 2010 09:07:59 -0400 MIME-Version: 1.0 Sent to CCL by: "Alavi, Saman" [Saman.Alavi ~~ nrc-cnrc.gc.ca] --_000_001A8CD833A9894A8AED786976F900240F09C435NRCCENMB1nrcca_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Sanjay, The Cambridge Cluster Database of David Wales has this information for some= metals and up to limited sizes. http://www-wales.ch.cam.ac.uk/CCD.html Best regards, Saman ________________________________ > From: owner-chemistry+saman.alavi=3D=3Dnrc.ca#,#ccl.net [owner-chemistry+sama= n.alavi=3D=3Dnrc.ca#,#ccl.net] On Behalf Of Sanjay Bharathwaj computationalch= emist_._gmail.com [owner-chemistry#,#ccl.net] Sent: June 5, 2010 1:26 AM To: Alavi, Saman Subject: CCL: Nanoparticles Dear Friends, I am trying to find a database where i can download structure of metal clus= ters and nanoparticles, with difference size and symmetry in the form of cartesian coordinates. Could any one help. My best regards, Dr. Sanjay --_000_001A8CD833A9894A8AED786976F900240F09C435NRCCENMB1nrcca_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi Sanj= ay,
 
The Cambridge Cluster Dat= abase of David Wales has this information for some metals and up to limited= sizes.
http://www-wales.ch.cam.ac.uk/CCD.html=
 
Best regards,
Saman
 
From: owner-chemistry+saman.ala= vi=3D=3Dnrc.ca#,#ccl.net [owner-chemistry+saman.alavi=3D=3Dnrc.ca#,#ccl.net= ] On Behalf Of Sanjay Bharathwaj computationalchemist_._gmail.com [owner-ch= emistry#,#ccl.net]
Sent: June 5, 2010 1:26 AM
To: Alavi, Saman
Subject: CCL: Nanoparticles

Dear Friends,

I am trying to find a database where i can download structure of metal= clusters and nanoparticles,
with difference size and symmetry in the form of cartesian coordinates= .

Could any one help.

My best regards,
Dr. Sanjay
--_000_001A8CD833A9894A8AED786976F900240F09C435NRCCENMB1nrcca_-- From owner-chemistry@ccl.net Sun Jun 6 14:32:00 2010 From: "Heath Matlock heathmatlock a gmail.com" To: CCL Subject: CCL: Nanoparticles Message-Id: <-42065-100606021924-24122-3Bgv28Vz/0h018aNY8dyaA*_*server.ccl.net> X-Original-From: Heath Matlock Content-Type: text/plain; charset=ISO-8859-1 Date: Sun, 6 Jun 2010 00:11:54 -0500 MIME-Version: 1.0 Sent to CCL by: Heath Matlock [heathmatlock]~[gmail.com] On Sat, Jun 5, 2010 at 12:26 AM, Sanjay Bharathwaj computationalchemist_._gmail.com wrote: > Dear Friends, > I am trying to find a database where i can download structure of metal > clusters and nanoparticles, > with difference size and symmetry in the form of cartesian coordinates. If you happen to find anything like this or end up making it yourself, please let me know. It's certainly of interest to me. -- Heath Matlock http://tweaklabs.org/Heath+Matlock