From chemistry-request@www.ccl.net Thu Feb 4 11:34:57 1999 From: "Stefan Fau" To: "CCL" Subject: Q:choosing "zero freqs" to be projected out Date: Thu, 4 Feb 1999 17:36:40 +0100 Dear CCLers, Gaussian (like many other programs) projects out the 6 "zero freqs" that belong to translation and rotation of a non-linear molecule before diagonalizing the remaining matrix. These "zero freqs" can be of similar magnitude as the lowest vibrational frequencies if the molecule is very floppy (I once had a molecule with 7 freqs of |ny|<15cm^-1). Does anybody know how the "zero freqs" are selected? Just by the absolute value of the raw frequency or is there some check for the type of movement (e.g. all atomic vectors of the mode parallel/orthogonal to the molecular translation/rotation vector) to avoid projecting out a vibrational frequency if vibrational and "zero" freqs are intermingled? I'll summarize if there is demand. Stefan ___________________________________ Dr. Stefan Fau Fachbereich Chemie, AK Frenking Philipps-Universität Marburg 35032 Marburg, Germany fau@chemie.uni-marburg.de