CCL:G: Problem with calculation of IR frequency at different temperature

From: John Keller <jwkeller~!~alaska.edu>
Subject: CCL:G: Problem with calculation of IR frequency at different temperature
Date: Thu, 26 Dec 2013 19:21:25 -0900

 Sent to CCL by: John Keller [jwkeller-$-alaska.edu]
 Hi Geetha,
 Ir frequencies, orbital energies, electron motions in orbitals are not
 temperature dependent. An atom is an atom whatever the temp. What does
 change with T is distribution of vibrational excited states. Close
 absolute zero, only lowest vibrational levels are populated. As the
 temperature rises,more and more of the upper states, which have larger
 amplitudes, are populated. At really high temps, the bonds break when
 the amplitudes get too large to hold the atoms together.
 John Keller
 Sent from my iPad
 > On Dec 26, 2013, at 6:11 PM, "Geetha Gopakumar Nair
 gopakumargeetha[a]gmail.com" <owner-chemistry:+:ccl.net> wrote:
 >
 >
 > Sent to CCL by: "Geetha Gopakumar Nair" [gopakumargeetha()
 gmail.com]
 > Hi
 >
 > I am working on water molecule using Gaussian09. I was trying to do the IR
 frequency calculations at
 > different temperatures. First I optimised and calculated the frequency at
 STP. Later using the optimised
 > structure, I tried different temperatures. I find the output printing
 correct temperatures but the
 > frequencies and their IR intensities remaining the same. Here with I have
 attached the necessary parts
 > of the run.
 >
 > best
 > Geetha
 >
 >
 > Run1.
 >
 > # PBE1PBE/CC-PVQZ opt freq
 >    1    2    3
 >    A1    A1    B2
 > Frequencies --    1638.9412    3867.1523    3970.9138
 > Red. masses --    1.0829    1.0449    1.0821
 > Frc consts  --    1.7139    9.207    10.0527
 > IR Inten    --    73.922    5.1287    57.1266
 >
 > Temperature   298.150 Kelvin.  Pressure   1.00000 Atm.
 >
 > Run2
 >
 > # PBE1PBE/CC-PVQZ opt freq=ReadIsotopes Temperature=500 Pressure=1
 >        1    2    3
 >        A1    A1    B2
 > Frequencies    --    1638.9412    3867.1523    3970.9138
 > Red. masses    --    1.0829    1.0449    1.0821
 > Frc consts    --    1.7139    9.207    10.0527
 > IR Inten    --    73.922    5.1287    57.1266
 >
 > Temperature   500.000 Kelvin.  Pressure   1.00000 Atm.>
 >