From owner-chemistry@ccl.net Tue Dec 10 01:55:00 2024 From: "Grigoriy Zhurko reg_zhurko ~ chemcraftprog.com" To: CCL Subject: CCL:G: Atomic masses used in Orca for computing vibrational frequencies Message-Id: <-55280-241210014036-16737-LMh7cOshsfzOtwrUoSnr0w:-:server.ccl.net> X-Original-From: Grigoriy Zhurko Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=utf-8 Date: Tue, 10 Dec 2024 09:40:04 +0300 MIME-Version: 1.0 Sent to CCL by: Grigoriy Zhurko [reg_zhurko . chemcraftprog.com] > I wonder if the deviations you observe might be related to whether or not the translations and rotations are projected out before computing the frequencies. Different program may adopt slightly different algorithms at this stage, possibly explaining these discrepancies. In such a case, the discrepancies would be molecule-dependent and perhaps even frequency-dependent within a given molecule. Are they? Is the C-12 “effective mass” of 12.00044 amu that you obtained from Orca by “reverse-engineering" identical for (a) different normal modes of the same molecule? (b) different carbon-only molecules, like C2, C3, C4? You are right that currently Chemcraft does not project out rotational and translational frequencies, but the difference seems to be very small: almosl full agreement is achieved when I compare the results produced by Chemcraft and by Gaussian 09. Here is a fragment of Gaussian output file for C2H5OH: Low frequencies --- -13.5962 -0.0008 0.0016 0.0020 15.8320 24.2907 Low frequencies --- 239.9425 302.8612 414.3268 Diagonal vibrational polarizability: 5.2307429 1.4851902 57.0611300 Harmonic frequencies (cm**-1), IR intensities (KM/Mole), Raman scattering activities (A**4/AMU), depolarization ratios for plane and unpolarized incident light, reduced masses (AMU), force constants (mDyne/A), and normal coordinates: 1 2 3 A" A" A' Frequencies -- 239.9211 302.8605 414.3261 Red. masses -- 1.1512 1.0693 2.6951 Frc consts -- 0.0390 0.0578 0.2726 IR Inten -- 34.6077 137.6567 15.2192 Atom AN X Y Z X Y Z X Y Z 1 6 0.00 0.00 0.06 0.00 0.00 0.05 -0.01 -0.19 0.00 2 1 -0.03 -0.07 0.11 0.01 -0.03 0.08 0.04 -0.18 -0.01 The frequencies at the top part of the fragment are without projecting out the r t freqs, and the value of e.g. 239.9425 is the same as produced by Chemcraft. The value 239.9211 is obtained by Gaussian after projecting r t out, and the difference is very small. For big frequencies, the difference between the freqs computed by Gaussian and Chemcraft is less than 0.0001 cm-1. a), b) - probably yes. I have computed the frequencies of CH3OH from Orca hess file, taking these masses (obtained by “reverse-engineering"): 12.0114368794449 for C 1.00803666900639 for H 15.9995819522312 for O With these masses, the frequencies computed by Chemcraft and Orca differ not more than 0.0001 cm-3 So I think it's even possible that I found some bug in Orca. Grigoriy