Subject: normal vibrations

From: [email-masked] (Ferenc Molnar)
Date: Wed, 30 Aug 95 18:23:21 +0200

Dear Netters:

I have a (maybe trivial) question concerning the calculation
of normal modes in MOPAC.

The diagonalization of the force matrix (in mass weighted
coordinates) leaves you with a set of eigenvalues and normal 
coordinates.

The eigenvalue number k correspond to (w_k)^2, where the w_ks
are the vibrational frequencies, this means:

 (w_k)^2=K_k/M_k 

K_k: force constant of the kth normal mode
M_k: reduced mass of the k_th normal mode

Now my question is, if (w_k)^2 determines only the ratio
of K_k and M_k, then how are the reduced masses, reported
in the "vibrational analysis" section of the MOPAC output 
file, calculated? Is there a convention, which "fraction" of
(w_k)^2 to use for K_k and which for M_k?

Thank you very much in advance!

Best regards,

Ferenc

Ferenc Molnar

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