From owner-chemistry@ccl.net Tue Jan 2 01:20:00 2018 From: "Andreas Klamt klamt##cosmologic.de" To: CCL Subject: CCL: Reference for structural details not amenable to forcefield analysis? Message-Id: <-53126-180102010746-24296-9uyTKHvY3WMOF07rWY6eDg**server.ccl.net> X-Original-From: Andreas Klamt Content-Language: de-DE Content-Type: multipart/alternative; boundary="------------EAF1108983B2856C7D045151" Date: Tue, 2 Jan 2018 07:07:35 +0100 MIME-Version: 1.0 Sent to CCL by: Andreas Klamt [klamt-#-cosmologic.de] This is a multi-part message in MIME format. --------------EAF1108983B2856C7D045151 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Joe, what forcefields can describe ornot depends on the forcefield you choose. Some people fit forcefields to quantum chemical interaction energies of the molecules, they want to simulate. By that you will be able to catch most effects. But most likely your question is where typical forcefields fail. My standard example is bromoform: Standard forcefields will describe the electrostatics by point charges, i.e. typically a negative point charge on halogens. Thus the most negative points on the the surface of bromoform are the tops of the bromine atoms. But if you look quantum chemically on bromoform, e.g. for the polarization charge density sigma on a COSMO surface, or the electrostatic potential on an iso-electrondensity surface, you will find that bromoform has even positive polarity at the top. And indeed, halogens are known to form interations with negative atoms, e.g. the lonepairs of oxygens, in crystal structures. This is the so-called halogen bonding effect, resulting from the so called sigma-hole, the electron depletion at the opposite side of sigma bonds. Forcefields based on point charge electrostatics are unable to describe this. Best regards Andreas Am 01.01.2018 um 20:32 schrieb Joe Leonard jleonard42-#-gmail.com: > Folks, does anybody have a (recent) reference to a study discussing > forcefield difficulties reproducing things like 1-5 interactions - > things that are well-modeled by QM but not by forcefields… > > Thanks in advance! And happy new year! > > Joe Leonard > jleonard42~~gmail.com > — > What's the difference between hardware and software? If you > use hardware long enough, it breaks. If you use software long enough, > it works. > > > -- Join us at the 5th-COSMO-RS-Symposium March 2018 Details at www.cosmologic.de/symposium_2018.html -------------------------------------------------- Prof. Dr. Andreas Klamt CEO / Geschäftsführer COSMOlogic GmbH & Co. KG Imbacher Weg 46 D-51379 Leverkusen, Germany phone +49-2171-731681 fax +49-2171-731689 e-mail klamt()cosmologic.de web www.cosmologic.de [University address: Inst. of Physical and Theoretical Chemistry, University of Regensburg] HRA 20653 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt Komplementaer: COSMOlogic Verwaltungs GmbH HRB 49501 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt --------------EAF1108983B2856C7D045151 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit

Joe,

what forcefields can describe ornot depends on the forcefield you choose. Some people fit forcefields to quantum chemical interaction energies of the molecules, they want to simulate. By that you will be able to catch most effects. But most likely your question is where typical forcefields fail.

My standard example is bromoform: Standard forcefields will describe the electrostatics by point charges, i.e. typically a negative point charge on halogens. Thus the most negative points on the the surface of bromoform are the tops of the bromine atoms. But if you look quantum chemically on bromoform, e.g. for the polarization charge density sigma on a COSMO surface, or the electrostatic potential on an iso-electrondensity surface, you will find that bromoform has even positive polarity at the top. And indeed, halogens are known to form interations with negative atoms, e.g. the lonepairs of oxygens, in crystal structures. This is the so-called halogen bonding effect, resulting from the so called sigma-hole, the electron depletion at the opposite side of sigma bonds.
Forcefields based on point charge electrostatics are unable to describe this.

Best regards

Andreas

Am 01.01.2018 um 20:32 schrieb Joe Leonard jleonard42-#-gmail.com:

Folks, does anybody have a (recent) reference to a study discussing forcefield difficulties reproducing things like 1-5 interactions - things that are well-modeled by QM but not by forcefields…

Thanks in advance! And happy new year!

Joe Leonard

jleonard42~~gmail.com

—

What's the difference between hardware and software? If you use hardware long enough, it breaks. If you use software long enough, it works.

-- 

Join us at the 5th-COSMO-RS-Symposium March 2018
Details at www.cosmologic.de/symposium_2018.html
--------------------------------------------------

Prof. Dr. Andreas Klamt
CEO / Geschäftsführer
COSMOlogic GmbH & Co. KG
Imbacher Weg 46
D-51379 Leverkusen, Germany

phone  	+49-2171-731681
fax    	+49-2171-731689
e-mail 	klamt()cosmologic.de
web    	www.cosmologic.de

[University address:      Inst. of Physical and
Theoretical Chemistry, University of Regensburg]

HRA 20653 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt
Komplementaer: COSMOlogic Verwaltungs GmbH
HRB 49501 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt

--------------EAF1108983B2856C7D045151-- From owner-chemistry@ccl.net Tue Jan 2 06:58:00 2018 From: "Mohamed E. A. Safy m.safy-x-compchem.net" To: CCL Subject: CCL: Reference for structural details not amenable to forcefield analysis? Message-Id: <-53127-180102065339-10263-j8kt1egSn+HN11jh5UgsEw#,#server.ccl.net> X-Original-From: "Mohamed E. A. Safy" Date: Tue, 2 Jan 2018 06:53:35 -0500 Sent to CCL by: "Mohamed E. A. Safy" [m.safy],[compchem.net] Dear CCl users Merry Christmas and happy new year for all of you, Halogen bonding in terms of Molecular Mechanics can be described using a new approach called positive extra point (PEP) approach. Inside PEP approach sigma-hole of halogen atom was represented by an extra-point (EP) of charge. More details about PEP approach can be found at the following links: https://link.springer.com/article/10.1007/s00894-012-1454-8 http://onlinelibrary.wiley.com/doi/10.1002/jcc.21836/full http://pubs.acs.org/doi/abs/10.1021/jp3003905 M.Safy From owner-chemistry@ccl.net Tue Jan 2 10:38:00 2018 From: "Andreas Klamt klamt%x%cosmologic.de" To: CCL Subject: CCL: Reference for structural details not amenable to forcefield analysis? Message-Id: <-53128-180102090742-18823-KjN3zK6c90QbFuofj0PwUw-$-server.ccl.net> X-Original-From: Andreas Klamt Content-Language: de-DE Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=utf-8 Date: Tue, 2 Jan 2018 15:07:30 +0100 MIME-Version: 1.0 Sent to CCL by: Andreas Klamt [klamt- -cosmologic.de] ... no question, as I already wrote, by special fitting and addition of special correction terms forcefields are able to reproduce every effect. But that is like predicting the weather of yesterday. As long as the electrostatics in forcefields is mainly described by the crude concept of atom centered point charges, they will in geral fail regarding the directionality of the electrostatics. The papers you mention describe local fits of corrections, which surely will correct nicely the deficiency they are made for, but in many other cases the deficiencies remain, because it is practically impossible to use these corrections for all atom types. Best regards Andreas Am 02.01.2018 um 12:53 schrieb Mohamed E. A. Safy m.safy-x-compchem.net: > Sent to CCL by: "Mohamed E. A. Safy" [m.safy],[compchem.net] > Dear CCl users > Merry Christmas and happy new year for all of you, > Halogen bonding in terms of Molecular Mechanics can be described using a new > approach called positive extra point (PEP) approach. Inside PEP approach > sigma-hole of halogen atom was represented by an extra-point (EP) of charge. > More details about PEP approach can be found at the following links: > https://link.springer.com/article/10.1007/s00894-012-1454-8 > http://onlinelibrary.wiley.com/doi/10.1002/jcc.21836/full > http://pubs.acs.org/doi/abs/10.1021/jp3003905 > M.Safy> > > -- Join us at the 5th-COSMO-RS-Symposium March 2018 Details at www.cosmologic.de/symposium_2018.html -------------------------------------------------- Prof. Dr. Andreas Klamt CEO / Geschäftsführer COSMOlogic GmbH & Co. KG Imbacher Weg 46 D-51379 Leverkusen, Germany phone +49-2171-731681 fax +49-2171-731689 e-mail klamt(~)cosmologic.de web www.cosmologic.de [University address: Inst. of Physical and Theoretical Chemistry, University of Regensburg] HRA 20653 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt Komplementaer: COSMOlogic Verwaltungs GmbH HRB 49501 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt From owner-chemistry@ccl.net Tue Jan 2 15:01:00 2018 From: "Hans-Ullrich SIEHL ullrich.siehl..uni-ulm.de" To: CCL Subject: CCL: electrostatics in force-fields Re: CCL: Reference for structural details not amenable to forcefield analysis? Message-Id: <-53129-180102141213-9119-1W9+lCLSjd1b8fIfja2BJg++server.ccl.net> X-Original-From: Hans-Ullrich SIEHL Content-Language: en-US Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=utf-8; format=flowed Date: Tue, 2 Jan 2018 20:12:08 +0100 MIME-Version: 1.0 Sent to CCL by: Hans-Ullrich SIEHL [ullrich.siehl|uni-ulm.de] To get rid of the limitation of fixed charges im MM calculations, the consistent charge equilibration method (CQEq) has been introduced. We have applied this concept to a special group of ionic liquids. "An application of the consistent charge equilibration (CQEq) method to guanidinium ionic liquid systems Chemical Physics Letters, Volume 457, Issue 1, p. 263-266. DOI:10.1016/j.cplett.2008.03.087 best regards Ulli -- send from: On 02.01.2018 15:07, Andreas Klamt klamt%x%cosmologic.de wrote: > > Sent to CCL by: Andreas Klamt [klamt- -cosmologic.de] > ... no question, as I already wrote, by special fitting and addition of > special correction terms forcefields are able to reproduce every effect. > But that is like predicting the weather of yesterday. As long as the > electrostatics in forcefields is mainly described by the crude concept > of atom centered point charges, they will in geral fail regarding the > directionality of the electrostatics. The papers you mention describe > local fits of corrections, which surely will correct nicely the > deficiency they are made for, but in many other cases the deficiencies > remain, because it is practically impossible to use these corrections > for all atom types. > > Best regards > > Andreas > > Am 02.01.2018 um 12:53 schrieb Mohamed E. A. Safy m.safy-x-compchem.net: >> Sent to CCL by: "Mohamed E. A. Safy" [m.safy],[compchem.net] >> Dear CCl users >> Merry Christmas and happy new year for all of you, >> Halogen bonding in terms of Molecular Mechanics can be described using a new >> approach called positive extra point (PEP) approach. Inside PEP approach >> sigma-hole of halogen atom was represented by an extra-point (EP) of charge. >> More details about PEP approach can be found at the following links: >> https://link.springer.com/article/10.1007/s00894-012-1454-8 >> http://onlinelibrary.wiley.com/doi/10.1002/jcc.21836/full >> http://pubs.acs.org/doi/abs/10.1021/jp3003905 >> M.Safy> >> >> >