From owner-chemistry@ccl.net Mon Dec 4 05:32:00 2023 From: "Grigoriy Zhurko reg_zhurko~~chemcraftprog.com" To: CCL Subject: CCL: Calculation of Gibbs energies of molecules with small frequencies Message-Id: <-55039-231204045312-25082-8teP1pLOtMmKbNL5aCd0IA]_[server.ccl.net> X-Original-From: Grigoriy Zhurko Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=windows-1250 Date: Mon, 4 Dec 2023 12:52:48 +0300 MIME-Version: 1.0 Sent to CCL by: Grigoriy Zhurko [reg_zhurko---chemcraftprog.com] I have implemented in my program Chemcraft a tool for computing the vibrational entropies and total Gibbs energies of molecules with small frequencies, using the frequencies threshold: all frequencies smaller than e.g. 100 cm-1 become 100 cm-1, so that the anharmonic effects which spoil the total entropy become less. I found that with this approach, the results agree better with the experiment, but currently I am unable to publish these results. And I have a stupid problem: I don�t remember what to cite for confirming the applicability of this approach (the help of low frequencies threshold). I remember that I had read about this somewhere, but I don�t remember when. Can you provide such a citation? Another question � what approaches alternative to this exist, and whether they are better. I have heard that Orca uses �QRRHO� approach; I have also watched the article of Grimme and Pracht who provided one more formula for small frequencies; probably this is called msRRHO. These are not the same approach? How good they are in comparison to applying a simple threshold? Grigoriy Zhurko https://chemcraftprog.com From owner-chemistry@ccl.net Mon Dec 4 07:51:01 2023 From: "=?utf-8?B?TWFyaXVzeiBSYWRvxYQ=?= mariusz.radon{}uj.edu.pl" To: CCL Subject: CCL: Calculation of Gibbs energies of molecules with small frequencies Message-Id: <-55040-231204074747-30267-wIPDuD3dEUowPwO3FMnNaA() server.ccl.net> X-Original-From: =?utf-8?B?TWFyaXVzeiBSYWRvxYQ=?= Content-Language: en-US Content-Type: multipart/signed; boundary="Apple-Mail=_73A002BF-F8EE-4051-84F3-3D1E7BDA9832"; protocol="application/pgp-signature"; micalg=pgp-sha256 Date: Mon, 4 Dec 2023 12:47:31 +0000 MIME-Version: 1.0 Sent to CCL by: =?utf-8?B?TWFyaXVzeiBSYWRvxYQ=?= [mariusz.radon:uj.edu.pl] --Apple-Mail=_73A002BF-F8EE-4051-84F3-3D1E7BDA9832 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 Dear Grigoriy: to my best knowledge, the quasi-harmonic approach you described was = first mentioned in this paper: Ribeiro, R. F.; Marenich, A. V.; Cramer, C. J. & Truhlar, D. G. "Use of Solution-Phase Vibrational Frequencies in Continuum Models for = the Free Energy of Solvation=E2=80=9D J. Phys. Chem. B, 2011, 115, = 14556-14562 I recently included a short discussion of alternative quasi-harmonic = approaches in the context of spin-state energetics (spin crossover) in a = PCCP Perspective (10.1039/D3CP03537A). Due to the specific context, I am = not directly addressing your question in general, but perhaps some of = the references cited will be relevant for you. Best wishes, Mariusz Radon -- Mariusz Radon, Ph.D., D.Sc. Associate Professor Faculty of Chemistry, Jagiellonian University Address: Gronostajowa 2, 30-387 Krakow, Poland Room C1-06, Phone: 48-12-686-24-89 E-mail: mradon ~ chemia.uj.edu.pl (mariusz.radon ~ uj.edu.pl) Web: https://tungsten.ch.uj.edu.pl/~mradon ORCID: https://orcid.org/0000-0002-1901-8521 > On 4 Dec 2023, at 10:52, Grigoriy Zhurko reg_zhurko~~chemcraftprog.com = wrote: >=20 >=20 >=20 > UWAGA: Wiadomo=C5=9B=C4=87 pochodzi od zewn=C4=99trznego nadawcy. >=20 >=20 >=20 > Sent to CCL by: Grigoriy Zhurko [reg_zhurko---chemcraftprog.com] > I have implemented in my program Chemcraft a tool for computing the = vibrational entropies and total Gibbs energies of molecules with small = frequencies, using the frequencies threshold: all frequencies smaller = than e.g. 100 cm-1 become 100 cm-1, so that the anharmonic effects which = spoil the total entropy become less. I found that with this approach, = the results agree better with the experiment, but currently I am unable = to publish these results. And I have a stupid problem: I don=E2=80=99t = remember what to cite for confirming the applicability of this approach = (the help of low frequencies threshold). I remember that I had read = about this somewhere, but I don=E2=80=99t remember when. Can you provide = such a citation? > Another question =E2=80=93 what approaches alternative to this exist, = and whether they are better. I have heard that Orca uses =E2=80=9CQRRHO=E2= =80=9D approach; I have also watched the article of Grimme and Pracht = who provided one more formula for small frequencies; probably this is = called msRRHO. These are not the same approach? How good they are in = comparison to applying a simple threshold? > Grigoriy Zhurko > https://chemcraftprog.com >=20 >=20 >=20 > -=3D This is automatically added to each message by the mailing script = =3D- > To recover the email address of the author of the message, please = change>=20>=20>=20>=20>=20> Conferences: = http://server.ccl.net/chemistry/announcements/conferences/ >=20>=20>=20>=20 >=20 --Apple-Mail=_73A002BF-F8EE-4051-84F3-3D1E7BDA9832 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP -----BEGIN PGP SIGNATURE----- iHUEAREIAB0WIQR+DG5LsRgBNXmBGWCmgNuaxEDwbQUCZW3KYgAKCRCmgNuaxEDw bS/tAP9GMtrscpmsbaclP5SZYUlgMiFk5LiaVlA8wNscNB/zDgEAjsuIYy7OCvsv F8jYKpyEeWP//b6CcTNoijWmdeL5x+U= =PqZO -----END PGP SIGNATURE----- --Apple-Mail=_73A002BF-F8EE-4051-84F3-3D1E7BDA9832-- From owner-chemistry@ccl.net Mon Dec 4 12:15:00 2023 From: "Frank Jensen frj**chem.au.dk" To: CCL Subject: CCL: Calculation of Gibbs energies of molecules with small frequencies Message-Id: <-55041-231204110231-4783-RX9hCPcQcyvQd6rHwJRhqA]_[server.ccl.net> X-Original-From: Frank Jensen Content-Language: en-US Content-Type: multipart/alternative; boundary="_000_DU2PR01MB79144FFCA27B7F2B195843219C86ADU2PR01MB7914eurp_" Date: Mon, 4 Dec 2023 16:02:05 +0000 MIME-Version: 1.0 Sent to CCL by: Frank Jensen [frj^chem.au.dk] --_000_DU2PR01MB79144FFCA27B7F2B195843219C86ADU2PR01MB7914eurp_ Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable Within the harmonic approximation, atomic motions associated with frequenci= es below 100 cm-1 often correspond to internal rotations around single bond= s. As the frequency goes towards zero, the entropy goes towards infinity, w= hile the correct limit for a free rotor is R/2. The approaches by Truhlar a= nd Grimme try to interpolate between the high frequency limit where the har= monic approximation is fair, and the free rotor limit. Use google to search= for papers from these groups. I do believe that this is a better approach = than simply setting all frequencies below 100 cm-1 to be 100 cm-1, and use = the harmonic approximation, although it certainly is better than doing noth= ing. How to interpolate, however, is a choice, and thus different groups en= d up with different formulas and results. Rotations around single bond are typically hindered, not free, rotors, and = the R/2 limit may thus be problematic, but calculating the H and S for hind= ered rotations requires the full rotational profile, and is thus substantia= lly more involved. Note also that for loosely bound complexes there may be several/many low fr= equency modes that do not correspond to internal rotations, but to liberati= on modes. As far as I know, nobody has looked at interpolating between the = harmonic approximation and the free translational limit for such cases, but= I would be interested in knowing if anybody has looked into this. Frank Frank Jensen Assoc. Prof. Dept. of Chemistry Aarhus University https://tildeweb.au.dk/au23758/ ________________________________ > From: owner-chemistry+frj=3D=3Dchem.au.dk{:}ccl.net on behalf of Grigoriy Zhurko reg_zhurko~~chemcraftpr= og.com Sent: Monday, December 4, 2023 10:52 AM To: Frank Jensen Subject: CCL: Calculation of Gibbs energies of molecules with small frequen= cies Sent to CCL by: Grigoriy Zhurko [reg_zhurko---chemcraftprog.com] I have implemented in my program Chemcraft a tool for computing the vibrati= onal entropies and total Gibbs energies of molecules with small frequencies= , using the frequencies threshold: all frequencies smaller than e.g. 100 cm= -1 become 100 cm-1, so that the anharmonic effects which spoil the total en= tropy become less. I found that with this approach, the results agree bette= r with the experiment, but currently I am unable to publish these results. = And I have a stupid problem: I don=92t remember what to cite for confirming= the applicability of this approach (the help of low frequencies threshold)= . I remember that I had read about this somewhere, but I don=92t remember w= hen. Can you provide such a citation? Another question =96 what approaches alternative to this exist, and whether= they are better. I have heard that Orca uses =93QRRHO=94 approach; I have = also watched the article of Grimme and Pracht who provided one more formula= for small frequencies; probably this is called msRRHO. These are not the s= ame approach? How good they are in comparison to applying a simple threshol= d? Grigoriy Zhurko https://chemcraftprog.com -=3D This is automatically added to each message by the mailing script =3D-http://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt--_000_DU2PR01MB79144FFCA27B7F2B195843219C86ADU2PR01MB7914eurp_ Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable

Within the harmonic approximation, atomic motions associated with frequenci= es below 100 cm-1 often correspond to internal rotations around single bond= s. As the frequency goes towards zero, the entropy goes towards infinity, w= hile the correct limit for a free rotor is R/2. The approaches by Truhlar and Grimme try to interpolate betw= een the high frequency limit where the harmonic approximation is fair, and = the free rotor limit. Use google to search for papers from these groups. I = do believe that this is a better approach than simply setting all frequencies below 100 cm-1 to be 100 cm-1= , and use the harmonic approximation, although it certainly is better than = doing nothing. How to interpolate, however, is a choice, and thus different= groups end up with different formulas and results.

Rotations around single bond are typically hindered, not free, rotors, and = the R/2 limit may thus be problematic, but calculating the H and S for hind= ered rotations requires the full rotational profile, and is thus substantia= lly more involved.

Note also that for loosely bound complexes there may be several/many low fr= equency modes that do not correspond to internal rotations, but to liberati= on modes. As far as I know, nobody has looked at interpolating between the = harmonic approximation and the free translational limit for such cases, but I would be interested in knowing i= f anybody has looked into this.

Frank

Frank Jensen
Assoc. Prof.
Dept. of Chemistry
Aarhus University
https://tildeweb.au.dk/au23758/<= /span>

=

From: owner-chemistry+frj= =3D=3Dchem.au.dk{:}ccl.net <owner-chemistry+frj=3D=3Dchem.au.dk{:}ccl.net>= ; on behalf of Grigoriy Zhurko reg_zhurko~~chemcraftprog.com <owner-chemistry{:}ccl.net>
Sent: Monday, December 4, 2023 10:52 AM
To: Frank Jensen <frj{:}chem.au.dk>
Subject: CCL: Calculation of Gibbs energies of molecules with small = frequencies

Sent to CCL by: Grigoriy Zhurko [reg_zhurko---chemcraftprog.com]
I have implemented in my program Chemcraft a tool for computing the vibrati= onal entropies and total Gibbs energies of molecules with small frequencies= , using the frequencies threshold: all frequencies smaller than e.g. 100 cm= -1 become 100 cm-1, so that the anharmonic effects which spoil the total entropy become less. I found that= with this approach, the results agree better with the experiment, but curr= ently I am unable to publish these results. And I have a stupid problem: I = don=92t remember what to cite for confirming the applicability of this approach (the help of low frequencies= threshold). I remember that I had read about this somewhere, but I don=92t= remember when. Can you provide such a citation?
Another question =96 what approaches alternative to this exist, and whether= they are better. I have heard that Orca uses =93QRRHO=94 approach; I have = also watched the article of Grimme and Pracht who provided one more formula= for small frequencies; probably this is called msRRHO. These are not the same approach? How good they are in co= mparison to applying a simple threshold?
Grigoriy Zhurko
https://chemcraftprog.com

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--_000_DU2PR01MB79144FFCA27B7F2B195843219C86ADU2PR01MB7914eurp_-- From owner-chemistry@ccl.net Mon Dec 4 14:42:01 2023 From: "Stefan Grimme grimme- -thch.uni-bonn.de" To: CCL Subject: CCL: Calculation of Gibbs energies of molecules with small frequencies Message-Id: <-55042-231204143919-23103-5kbmHH6CZ/ZJccfWnS9qgQ]_[server.ccl.net> X-Original-From: "Stefan Grimme" Date: Mon, 4 Dec 2023 14:39:16 -0500 Sent to CCL by: "Stefan Grimme" [grimme{:}thch.uni-bonn.de] As an addition to F. Jensens answer: we have carefully benchmarked our low-frequency rot-vib interpolation scheme (which is e.g. implemented in ORCA) for absolute gas phase entropies of molecules (calculation of absolute molecular entropies and heat capacities made simple, Chem. Sci., (2021), 12, 65516568. DOI: 10.1039/d1sc00621e) and found (with scaled harmonic DFT frequencies, i.e., msRRHO [modified, scaled] and including conformational terms) excellent agreement to experimental data with average deviations of 1 cal mol^-1 K^-1 (about 12%). Best Stefan From owner-chemistry@ccl.net Mon Dec 4 15:16:01 2023 From: "Sebastian Kozuch kozuch[#]bgu.ac.il" To: CCL Subject: CCL: Calculation of Gibbs energies of molecules with small frequencies Message-Id: <-55043-231204074849-30348-8VrmebTgOpDvoyUwVQCynQ{}server.ccl.net> X-Original-From: Sebastian Kozuch Content-Language: en-US Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8; format=flowed Date: Mon, 4 Dec 2023 14:48:31 +0200 MIME-Version: 1.0 Sent to CCL by: Sebastian Kozuch [kozuch!=!bgu.ac.il] Please check the work of Cramer and Truhlar for the 100 cm-1 approach: https://pubs.acs.org/doi/full/10.1021/jp205508z Also of interest can be the similar method of Grimme, which makes things smoother: https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.201200497 We tested both methods in a specific organometallic reaction and found that, as always, it depends. But using 50 cm-1 cutoff worked better for our case. See: https://pubs.acs.org/doi/full/10.1021/acs.jctc.3c00205 Best, Sebastian On 04/12/2023 11:52, Grigoriy Zhurko reg_zhurko~~chemcraftprog.com wrote: > Sent to CCL by: Grigoriy Zhurko [reg_zhurko---chemcraftprog.com] > I have implemented in my program Chemcraft a tool for computing the vibrational entropies and total Gibbs energies of molecules with small frequencies, using the frequencies threshold: all frequencies smaller than e.g. 100 cm-1 become 100 cm-1, so that the anharmonic effects which spoil the total entropy become less. I found that with this approach, the results agree better with the experiment, but currently I am unable to publish these results. And I have a stupid problem: I don’t remember what to cite for confirming the applicability of this approach (the help of low frequencies threshold). I remember that I had read about this somewhere, but I don’t remember when. Can you provide such a citation? > Another question – what approaches alternative to this exist, and whether they are better. I have heard that Orca uses “QRRHO” approach; I have also watched the article of Grimme and Pracht who provided one more formula for small frequencies; probably this is called msRRHO. These are not the same approach? How good they are in comparison to applying a simple threshold? > Grigoriy Zhurko > https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2fchemcraftprog.com&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-ceaa833146a0af31c823abf1a7129c79c3ec581c> https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fwww.ccl.net%2fcgi%2dbin%2fccl%2fsend%5fccl%5fmessage&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-ce4bf59ea9479f7e102500cd8fba68b06c6567fa> https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fwww.ccl.net%2fcgi%2dbin%2fccl%2fsend%5fccl%5fmessage&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-ce4bf59ea9479f7e102500cd8fba68b06c6567fa> https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fwww.ccl.net%2fchemistry%2fsub%5funsub.shtml&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-1b0c22bc98825d8b2ca19d54a25845bb63b42129 > > Before posting, check wait time at: https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fwww.ccl.net&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-2c7ae2cf3db92861a6e70d0d9fe98224f00dd965 > > Job: https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fwww.ccl.net%2fjobs&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-337f2de3b944ffbdbe31d47087416d72320adea2 > Conferences: https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fserver.ccl.net%2fchemistry%2fannouncements%2fconferences%2f&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-7f7a9fd0354d9dd5020a209fce935f69a67d4e57 > > Search Messages: https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fwww.ccl.net%2fchemistry%2fsearchccl%2findex.shtml&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-79526e619fe0b6c97ef1667ef2d03295a4eef4de> https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fwww.ccl.net%2fspammers.txt&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-f402c335da6ff3d2bd8f82041e114cc1319f9ae9 > > RTFI: https://imsva91-ctp.trendmicro.com:443/wis/clicktime/v1/query?url=http%3a%2f%2fwww.ccl.net%2fchemistry%2faboutccl%2finstructions%2f&umid=D69685C6-0BAD-3906-AC65-17BB71A9BAB7&auth=701951cf8dfb7cd99762e0f5be252082d875f1cf-6c2fa338fd6b05efa2550169fa9daff660921a8b > -- ‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗‗ .........Sebastian Kozuch......... ......Department of Chemistry..... Ben-Gurion University of the Negev .........kozuch*bgu.ac.il......... ......www.bgu.ac.il/~kozuch/...... ˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭˭ From owner-chemistry@ccl.net Mon Dec 4 15:51:01 2023 From: "Omar Valsson omar.valsson*o*gmail.com" To: CCL Subject: CCL: Calculation of Gibbs energies of molecules with small frequencies Message-Id: <-55044-231204090153-23796-RZCF51FZ6O/rBzJkAXRXQQ_._server.ccl.net> X-Original-From: Omar Valsson Content-Type: multipart/alternative; boundary="000000000000a69cf1060baf8e43" Date: Mon, 4 Dec 2023 08:01:29 -0600 MIME-Version: 1.0 Sent to CCL by: Omar Valsson [omar.valsson!=!gmail.com] --000000000000a69cf1060baf8e43 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hello, This description of the thermochemistry calculation options available in SEQCROW plugin for ChimeraX might help: https://github.com/QChASM/SEQCROW/wiki/Process-Thermochemistry-Tool According to this, what you are describing is what is there called the quasi-harmonic with reference to a paper by Truhlar et. al ( https://pubs.acs.org/doi/10.1021/jp205508z). The quasi-RRHO approximation should be the same as the one in ORCA. Best regards, Omar On Mon, Dec 4, 2023 at 6:23=E2=80=AFAM Grigoriy Zhurko reg_zhurko~~chemcraf= tprog.com wrote: > > Sent to CCL by: Grigoriy Zhurko [reg_zhurko---chemcraftprog.com] > I have implemented in my program Chemcraft a tool for computing the > vibrational entropies and total Gibbs energies of molecules with small > frequencies, using the frequencies threshold: all frequencies smaller tha= n > e.g. 100 cm-1 become 100 cm-1, so that the anharmonic effects which spoil > the total entropy become less. I found that with this approach, the resul= ts > agree better with the experiment, but currently I am unable to publish > these results. And I have a stupid problem: I don=E2=80=99t remember what= to cite > for confirming the applicability of this approach (the help of low > frequencies threshold). I remember that I had read about this somewhere, > but I don=E2=80=99t remember when. Can you provide such a citation? > Another question =E2=80=93 what approaches alternative to this exist, and= whether > they are better. I have heard that Orca uses =E2=80=9CQRRHO=E2=80=9D appr= oach; I have also > watched the article of Grimme and Pracht who provided one more formula fo= r > small frequencies; probably this is called msRRHO. These are not the same > approach? How good they are in comparison to applying a simple threshold? > Grigoriy Zhurko > https://chemcraftprog.com > > > > -=3D This is automatically added to each message by the mailing script = =3D-> > > --000000000000a69cf1060baf8e43 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

Hello,=C2=A0

This description=C2=A0of t= he thermochemistry calculation options available in SEQCROW plugin for Chim= eraX might help:

https://github.com/QChASM/SEQCROW/wiki/Proc= ess-Thermochemistry-Tool=C2=A0=C2=A0

=C2=A0

Acc= ording to this, what you are describing is what is there called the=C2=A0qu= asi-harmonic with reference to a paper by=C2=A0Truhlar et. al (https://pubs.acs.org/doi/10.1021= /jp205508z).=C2=A0The=C2=A0quasi-RRHO approximation should be the same = as the one in ORCA.

Best regards,

Omar= =C2=A0

On Mon, Dec 4, 2023 at 6:23=E2=80= =AFAM Grigoriy Zhurko reg_zhurko~~chem= craftprog.com <owner-chem= istry|a|ccl.net> wrote:

Sent to CCL by: Grigoriy Zhurko [reg_zhurko---chemcraftprog.com= ]
I have implemented in my program Chemcraft a tool for computing the vibrati= onal entropies and total Gibbs energies of molecules with small frequencies= , using the frequencies threshold: all frequencies smaller than e.g. 100 cm= -1 become 100 cm-1, so that the anharmonic effects which spoil the total en= tropy become less. I found that with this approach, the results agree bette= r with the experiment, but currently I am unable to publish these results. = And I have a stupid problem: I don=E2=80=99t remember what to cite for conf= irming the applicability of this approach (the help of low frequencies thre= shold). I remember that I had read about this somewhere, but I don=E2=80=99= t remember when. Can you provide such a citation?
Another question =E2=80=93 what approaches alternative to this exist, and w= hether they are better. I have heard that Orca uses =E2=80=9CQRRHO=E2=80=9D= approach; I have also watched the article of Grimme and Pracht who provide= d one more formula for small frequencies; probably this is called msRRHO. T= hese are not the same approach? How good they are in comparison to applying= a simple threshold?
Grigoriy Zhurko
= https://chemcraftprog.com

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--000000000000a69cf1060baf8e43-- From owner-chemistry@ccl.net Mon Dec 4 16:26:01 2023 From: "Philipp Pracht pp555.##.cam.ac.uk" To: CCL Subject: CCL: Calculation of Gibbs energies of molecules with small frequencies Message-Id: <-55045-231204124703-19875-m0zlEuFpBkvDHi426m//yA##server.ccl.net> X-Original-From: "Philipp Pracht" Date: Mon, 4 Dec 2023 12:46:59 -0500 Sent to CCL by: "Philipp Pracht" [pp555|,|cam.ac.uk] Dear Grigoriy, To answer the part about qRRHO in ORCA and msRRHO: They are the same thing. They refer to an interpolation of the vibrational entropy of the harmonic oscillator with the entropy of a free rotor and was first presented in Grimme, S. (2012), Chem.Eur.J., 18, 9955-9964. https://doi.org/10.1002/chem.201200497 The approach is called the quasi- or modified-RRHO (qRRHO or mRRHO) and compared to the 100cm^-1 cut-off it is a continuous treatment. It is slightly more work to implement it, but fairly straightforward. The "s" part in msRRHO we used in Pracht, P., Grimme, S. (2021), Chem. Sci., 12, 6551-6568. https://doi.org/10.1039/D1SC00621E refers the factor that is often used for (down-)scaling of frequencies in DFT calculations. Though, this is mostly for correcting higher frequency modes. See, for example, Merrick, J.P., Moran, D., Radom, L., (2007), JPCA, 111, 11683-11700. https://doi.org/10.1021/jp073974n If you are interested in calculating molecular entropy/Gibbs free energy as accurately as possible (and without going to anharmonic effects), you'd probably need both the high- and low-frequency treatment; possibly also a correction for conformational entropy. Best wishes, Philipp -- Dr. Philipp Pracht (pp555 _ cam.ac.uk) Yusuf Hamied Department of Chemistry University of Cambridge Lensfield Road, Cambridge CB2 1EW United Kingdom