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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Dear Molpro users and developers,<br>
<br>
As a new Molpro user I am experimenting with several features. Currently I want to understand better how to extract the spectroscopic parameters using "Diatomic" routine. To test the basics, I made the following table of bond length versus energy for a hypothetical
molecule with perfectly harmonic potential: reduced mass of 1u, equilibrium bond length of 1.6 angstrom, equilibrium energy of 1eV and a spring constant of 1eV/Angstrom^2:<br>
<br>
DIST ENRGY<br>
1.5000 1.0050000000<br>
1.5200 1.0032000000<br>
1.5400 1.0018000000<br>
1.5600 1.0008000000<br>
1.5800 1.0002000000<br>
1.6000 1.0000000000<br>
1.6200 1.0002000000<br>
1.6400 1.0008000000<br>
1.6600 1.0018000000<br>
1.6800 1.0032000000<br>
1.7000 1.0050000000<br>
<br>
The statistics subcommand of table command gives me<br>
===========<br>
Quadratic fit to 3 lowest: x0/y0/hessian<br>
1.6000000000<br>
1.0000016138<br>
1.0000000000<br>
===========<br>
<br>
Doing the unit conversion I find that the harmonic frequency of this molecule should be
<b>3276 cm-1</b>. See the wolfram alpha link here:<br>
<a href="http://www.wolframalpha.com/input/?i=sqrt%281+eV%2FAngstrom^2+%2F%281+u%29%29%2Fc+in+cm^-1" target="_blank">http://www.wolframalpha.com/input/?i=sqrt%281+eV%2FAngstrom^2+%2F%281+u%29%29%2Fc+in+cm^-1</a><br>
<br>
However the result of Diatomic is <br>
========================================================================================================<br>
ENRE RE(AU) RE(A) BE AE WE WEXE WEYE DE D0 SIG<br>
========================================================================================================<br>
1.0000000 3.0236 1.6000 6.585 -0.0956 <b>2720.23</b> 0.00 0.00 0.00 0.00 0.4812875E-16<br>
========================================================================================================<br>
<br>
As you see, the harmonic frequency w_e is found to be 2720. <br>
I do not understand where this difference comes from. I would greatly appreciate your help if you could point out what I am missing here.<br>
<br>
The input file:<br>
======================<br>
***,harmonic pot. k=1<br>
redm=1.0<br>
ii=0<br>
dr=0.02<br>
DO r=1.5,1.7,dr,ANG<br>
ii=ii+1<br>
dist(ii)=r<br>
enrgy(ii)=1+0.5*(r-1.6)*(r-1.6)<br>
ENDDO<br>
{table, dist, enrgy; digits, 4,10 ;statistics; diatomic,degree=2, MASS=redm}<br>
=================<br>
<br>
Thank you,<br>
emine kucukbenli, postdoc @ theos, epfl, switzerland <br>
<br>
<br>
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