From owner-chemistry@ccl.net Fri Dec 6 14:03:01 2024 From: "Grigoriy Zhurko reg_zhurko(-)chemcraftprog.com" To: CCL Subject: CCL:G: Atomic masses used in Orca for computing vibrational frequencies Message-Id: <-55264-241206100901-5028-Ds3Qor3mzsbk0vqkT4dE9A _ server.ccl.net> X-Original-From: Grigoriy Zhurko Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=windows-1250 Date: Fri, 6 Dec 2024 18:08:44 +0300 MIME-Version: 1.0 Sent to CCL by: Grigoriy Zhurko [reg_zhurko{=}chemcraftprog.com] Hello, I have asked this question at Orca forum, but they didn’t respond so I’d like to ask it here. I have implemented in my program reading files with the Hessian (Gaussian .fch and orca .hess files), and computing the vibrational frequencies in RRHO approximation using it. However, the frequencies computed by Chemcraft are slightly different from the ones computed by Orca (printed in the same .Hess file and in the output file). For example, for O3 molecule, the highest frequency printed by Orca is 1544.255736 cm-1, while with Chemcraft I got the value of 1544.283821. Initially, Chemcraft used the atomic mass of O atoms printed in the .hess file, which is 15.999. I found that I can get almost equal results as the ones produced by Orca, if I use the following values of atomic masses: 12.0114368794449 instead of 12.011 for C atoms; 15.9995819522312 instead of 15.999 for O atoms; 1.00803666900639 instead of 1.008 for H atoms. So it is not clear for me, what is the reason of this difference. Possibly Orca simply prints the masses with low precision; but it is not clear for me, where did it take e.g. the mass of 12.0114368794449 for C, while the most abundant isotope has the mass of 12.0000000. Gaussian uses these masses of most abundant isotopes (12.0 for C, 1.00782503223 for H, etc), and I got almost equal frequencies with Chemcraft and Gaussian. In the nature, for C atom we have two isotopes, 12.0000000 with 98.93% and 13.00335483507 with 1.07%, at average 12.0107358967352. You can see that this averaged mass still does not match the mass used in Orca. Grigoriy Zhurko chemcraftprog.com From owner-chemistry@ccl.net Fri Dec 6 15:30:01 2024 From: "Cory Pye Cory.Pye-x-smu.ca" To: CCL Subject: CCL:G: Atomic masses used in Orca for computing vibrational frequencies Message-Id: <-55265-241206152851-1268-CxYxVehmUy5TIDVFajM8hQ*|*server.ccl.net> X-Original-From: Cory Pye Content-Language: en-US Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" Date: Fri, 6 Dec 2024 20:28:39 +0000 MIME-Version: 1.0 Sent to CCL by: Cory Pye [Cory.Pye__smu.ca] Grigoriy, Could the difference be due to the mass difference between the nuclei and the atom (i.e. mass of electron * number of electrons)? -Cory -----Original Message----- > From: owner-chemistry+cory.pye==smu.ca###ccl.net On Behalf Of Grigoriy Zhurko reg_zhurko(-)chemcraftprog.com Sent: December 6, 2024 11:09 AM To: Cory Pye Subject: CCL:G: Atomic masses used in Orca for computing vibrational frequencies Sent to CCL by: Grigoriy Zhurko [reg_zhurko{=}chemcraftprog.com] Hello, I have asked this question at Orca forum, but they didn't respond so I'd like to ask it here. I have implemented in my program reading files with the Hessian (Gaussian .fch and orca .hess files), and computing the vibrational frequencies in RRHO approximation using it. However, the frequencies computed by Chemcraft are slightly different from the ones computed by Orca (printed in the same .Hess file and in the output file). For example, for O3 molecule, the highest frequency printed by Orca is 1544.255736 cm-1, while with Chemcraft I got the value of 1544.283821. Initially, Chemcraft used the atomic mass of O atoms printed in the .hess file, which is 15.999. I found that I can get almost equal results as the ones produced by Orca, if I use the following values of atomic masses: 12.0114368794449 instead of 12.011 for C atoms; 15.9995819522312 instead of 15.999 for O atoms; 1.00803666900639 instead of 1.008 for H atoms. So it is not clear for me, what is the reason of this difference. Possibly Orca simply prints the masses with low precision; but it is not clear for me, where did it take e.g. the mass of 12.0114368794449 for C, while the most abundant isotope has the mass of 12.0000000. Gaussian uses these masses of most abundant isotopes (12.0 for C, 1.00782503223 for H, etc), and I got almost equal frequencies with Chemcraft and Gaussian. In the nature, for C atom we have two isotopes, 12.0000000 with 98.93% and 13.00335483507 with 1.07%, at average 12.0107358967352. You can see that this averaged mass still does not match the mass used in Orca. Grigoriy Zhurko chemcraftprog.comhttp://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtml/http://www.ccl.net/spammers.txt