[molpro-user] normal mode
Eryin Feng
fengbf at mail.ahnu.edu.cn
Tue Jul 26 09:34:55 BST 2011
Dear users,
In my work, I try to get the normal mode coordinates of a molecule by molpro, but when i compare the result get from molpro with from Gaussian98 code, I find the different results !
For example: O--C--S (linear molecule), V3 antisymmetry normal mode (Q3) :
in Gaussian: Q3: -0.50 Oz + 0.86 Cz - 0.07 Sz ( molecule located at Z axis)
in molpro: Q3: -0.14098 Oz + 0.2364 Cz -0.01822 Sz
To switch from Molpro normal coordinate coefficient to gaussian one, two molpro-users told me two different methods as:
(1) calculate the reduced mass (mured) corresponding to the normal coordinate of interest.
mured= 1/sqrt( sum over all cartesian displacements of the square of the molpro coefficient divided by the corresponding atomic mass )
Here mured =1/sqrt [ (0.14098)^2/15.99 + (0.2364)^2/12 + (0.01822)^2/31.97]= 13.006
multiplying the molpro coeff. by 1 / sqrt(mured) gives the corresponding gaussian normal coordinate coefficient
This method gives:
reduced mass: 13.008
Q3: -5.084378723760641E-001 Oz + 8.526378218576923E-001 Cz - 6.570958769342700E-002 Sz
(2) The reduced mass can be calculated from 1/(sum-of-squares of molpro normal coordinate coefficient ):
mured= 1/( 0.14098^2 + 0.2364^2 + 0.01822^2 )= 13.14030
multiplying the molpro coeff. by 1 / sqrt(mured) gives the corresponding gaussian normal coordinate coefficient
This method gives:
reduced mass: 13.1403
Q3: -5.110462461425969E-001 Oz + 8.570120005877189E-001 Cz - 6.604668918421140E-002 Sz
The difference between these two method seems to origin from the different cognizance that the use or not of mass-weighted coordinates for Molpro normal coordinate coefficient . What is the true case in Molpro? (Which method is right ?) Looking forward to your suggestions!
Thanks in advance!
Eryin Feng
department of physics,
Anhui normal university,China
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