CCL:G: Gaussian IR frequency calculation



 Sent to CCL by: zborowsk [zborowsk^chemia.uj.edu.pl]
 W dniu 2015-03-23 19:26, ggotelli()kaliumtech.com napisał(a):
 
 Sent to CCL by: [ggotelli[]kaliumtech.com]
 Thank you all for your help!
 I'll condense all my notes in the same mail.
 Krzysztof , yes I observed the difference in the whole spectrum.
 
 
Well, something strange. 300-400 cm-1 difference between theory and experiment around 3000 cm-1 and also around 100 cm-1?? By the way, do you have positive or negative (imaginary) frequencies around 100???
 
 
Serdar, the molecule that I 'm trying to calculate and where I have the differences is a dimer derived from dilactide. To estimate a scaling factor my reference molecule is dilactide in itself, which in turn has little differences between the calculated spectrum and the real one, depending on
 the peaks.
 André, thanks for the scaling factor reference.
 
Stent, the polymer spectrum was made with an ATR device and without solvent.
 Because of this all calculations have done in vacuum.
 
Robert, thanks for all your comments, they made me realize that my error was
 trying to adjust a dimer spectrum to a polymer spectrum, what are, of
 
course, very different things. Although the dimer peaks are displaced with respect to those of the polymer, it can be seen from the GView animation that they correspond to what is expected, beyond the displacement involved.
 Regards!
 Gustavo Gotelli
 Polymer Synthesis
 Pharmaceutical Technology Department
 Faculty of Pharmacy and Biochemistry
 Buenos Aires University
 Argentina
 -----Mensaje original-----
 De: owner-chemistry+ggotelli==kaliumtech.com a ccl.net
 
[mailto:owner-chemistry+ggotelli==kaliumtech.com a ccl.net] En nombre de
 Víctor Luaña Cabal victor^^fluor.quimica.uniovi.es
 Enviado el: sábado, 21 de marzo de 2015 21:16
 Para: Gotelli, Gustavo A
 Asunto: CCL: Gaussian IR frequency calculation
 Sent to CCL by: =?iso-8859-1?Q?V=EDctor_Lua=F1a?= Cabal
 [victor]|[fluor.quimica.uniovi.es]
 On Sat, Mar 21, 2015 at 05:56:44PM -0400, Robert Molt
 r.molt.chemical.physics],[gmail.com wrote:
 
 Sent to CCL by: Robert Molt [r.molt.chemical.physics---gmail.com]
 
Moreover, you are using the B3LYP functional. It has limited accuracy, depending on the system specifics. If it is a multi-reference problem,
 great care is necessary.
 
Also note that you can only compare the TOTAL spectrum, not any one peak.
 Robert,
 1) Let me take your highly correct advise to remember to the newest
    generations that the role on computational chemistry is not being
    able to reproduce the number of the experiment.
 2) The experiment helps in modulating our calculations, and the final
    objective is a perfect reprodution of the experiment.
 3) But the reason is not substituting experiments. The reason is that
    in the processs of mimicking it we learn the rules that govern
    Nature.
 4) There are too many questions in this forum that tend to ignore
    this rule and it is important to remember it again and again.
 Best regards,
             Dr. Víctor Luaña
 --
      .  .    "The hardest part in solving a problem is recognizing
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   /`. \/ .'\          -- ¿?
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 |'`'`|  | actitud"
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 !            Dr.Víctor Luaña                 ! Mediocre is worse than
 ! Departamento de Química Física y Analítica ! good, but it is
 also !
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! e-mail: victor-#-fluor.quimica.uniovi.es ! mediocrity is not a grade,
 ! phone: +34-985-103491  fax: +34-985-103125 ! it is an attitude
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 Krzysztof K. Zborowski
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