Thank you very much for a reply,

Then instead of litium ion, I have to give charge on the whole system. W= ill=A0 that be correct?

Thanks,

Mohan

On Mon, Feb 10, 2014 at 9:12 PM, Susi Le= htola susi.lehtola|a|alumni.helsinki.= fi <owner-chemistry.||.ccl.net> wrote:

Sent to CCL by: Susi Lehtola [susi.lehtola++alumni.helsinki.fi]
On Mon, 10 Feb 2014 20:28:54 +0530
"Mohan maruthi sena maruthi.sena[*]gmail.com" <owner-chemistry++ccl.net>
wrote:

> Hi all,
> =A0 =A0 =A0 =A0 =A0 I have a system which contains acetone molecule an= d lithium ion.
> How can I specify that there is charge on the lithium ion in input fil= e for
> gaussian09. Is it enough if i mention at the beginning of the file =A0= charge
> 1 and spin 1.

You can't assign electronic charges to single atoms. Instead, the=
distribution of charge is determined by the quantum mechanical
calculation, and different methods will result in different partial
charges on the atoms. The charge is assigned to the whole system.

As you're using DFT its important to note that it will, in general,
not result in proper charge dissociation. See e.g. J. Chem. Phys. 125,
194112 (2006); doi: 10.1063/1.2387954.
--
---------------------------------------------------------------
Mr. Susi Lehtola, PhD =A0 =A0 =A0 =A0 =A0 =A0 Research Associate
susi.lehtola++alumn= i.helsinki.fi =A0 Department of Applied Physics
http://www.h= elsinki.fi/~jzlehtol =A0Aalto University
=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Finland=
---------------------------------------------------------------
Susi Lehtola, FT =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Tutkijatohtori
susi.lehtola++alumn= i.helsinki.fi =A0 Fysiikan laitos
http://www.h= elsinki.fi/~jzlehtol =A0Aalto-yliopisto
---------------------------------------------------------------

-=3D This is automatically added to each message by the mailing script =3D-=
E-mail to subscribers: CHEMISTRY.||.ccl.n= et or use:
=A0 =A0 =A0 http://www.ccl.net/cgi-bin/ccl/send_ccl_message

E-mail to administrators: CHEM= ISTRY-REQUEST.||.ccl.net or use
=A0 =A0 =A0 http://www.ccl.net/cgi-bin/ccl/send_ccl_message

Subscribe/Unsubscribe:
=A0 =A0 =A0 http://www.ccl.net/chemistry/sub_unsub.shtml

Before posting, check wait time at: http://www.ccl.net

Job: http://www.ccl.n= et/jobs
Conferences: http://server.ccl.net/chemistry/announcements/co= nferences/

Search Messages: http://www.ccl.net/chemistry/searchccl/index.shtml
=A0 =A0 =A0 h= ttp://www.ccl.net/spammers.txt

RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/

--047d7bfceb4a9fe9f204f2100cfe-- From owner-chemistry@ccl.net Mon Feb 10 13:48:01 2014 From: "Wendy Anne Warr wendy]~[warr.com" To: CCL Subject: CCL: Latest ACS Meeting Report Message-Id: <-49648-140210130538-17097-Z//UrwvJVlBRyivDiIaWLw ~~ server.ccl.net> X-Original-From: "Wendy Anne Warr" Date: Mon, 10 Feb 2014 13:05:36 -0500 Sent to CCL by: "Wendy Anne Warr" [wendy ~ warr.com] Chemical Information and Computation 2013, Number Two. 246th ACS National Meeting and Exposition, Indianapolis, IN, September 8-12, 2013 Our 42nd report in this series covers a selection of papers, in detail, from the following technical symposia: current challenges in cheminformatics: exploiting information and knowledge in structured and unstructured environments semantic technologies in translational medicine and drug discovery exchangeable molecular and analytical data formats and their importance in facilitating data exchange Herman Skolnik Award symposium 2013 honoring Richard D. (Dick) Cramer (Different format from rest of report; open access version at http://bulletin.acscinf.org/node/536). There is also the usual news section covering more than 60 companies. The report is over 200 pages long, in full color. Contents list and order forms at http://www.warr.com; over 50% discount to academia and government. Wendy Dr. Wendy A. Warr Wendy Warr & Associates 6 Berwick Court, Holmes Chapel Cheshire, CW4 7HZ, England Tel./Fax +44 (0)1477 533837 wendy:-:warr.com http://www.warr.com Skype: wendyannewarr Twitter: :-:WendyAnneWarr From owner-chemistry@ccl.net Mon Feb 10 14:23:00 2014 From: "Abrash, Samuel sabrash .. richmond.edu" To: CCL Subject: CCL:G: How to consider charge on particular atom -lithium Message-Id: <-49649-140210142031-24385-6lQRlmlMz9e7UmBL6YZJWg!^!server.ccl.net> X-Original-From: "Abrash, Samuel" Content-Language: en-US Content-Type: multipart/alternative; boundary="_000_A7C78D2AEE62DB40B9CB1ADE9D5990A2C2BFAB97quorrarichmonde_" Date: Mon, 10 Feb 2014 19:20:22 +0000 MIME-Version: 1.0 Sent to CCL by: "Abrash, Samuel" [sabrash=-=richmond.edu] --_000_A7C78D2AEE62DB40B9CB1ADE9D5990A2C2BFAB97quorrarichmonde_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable As an additional point, the final charge distributions (if using appropriat= e theoretical methods) do tend to follow basic chemical principles, so the = bulk of the charge will end up on whichever species has the lowest ionizati= on potential. Sam > From: owner-chemistry+sabrash=3D=3Drichmond.edu-.-ccl.net [mailto:owner-chemi= stry+sabrash=3D=3Drichmond.edu-.-ccl.net] On Behalf Of Mohan maruthi sena mar= uthi.sena/agmail.com Sent: Monday, February 10, 2014 11:44 AM To: Abrash, Samuel Subject: CCL:G: How to consider charge on particular atom -lithium Thank you very much for a reply, Then instead of litium ion, I have to give charge on the whole system. Will= that be correct? Thanks, Mohan On Mon, Feb 10, 2014 at 9:12 PM, Susi Lehtola susi.lehtola|a|alumni.helsink= i.fi

> wrote: Sent to CCL by: Susi Lehtola [susi.lehtola++alumni.helsinki.fi] On Mon, 10 Feb 2014 20:28:54 +0530 "Mohan maruthi sena maruthi.sena[*]gmail.com" > wrote: > Hi all, > I have a system which contains acetone molecule and lithium ion= . > How can I specify that there is charge on the lithium ion in input file f= or > gaussian09. Is it enough if i mention at the beginning of the file charg= e > 1 and spin 1. You can't assign electronic charges to single atoms. Instead, the distribution of charge is determined by the quantum mechanical calculation, and different methods will result in different partial charges on the atoms. The charge is assigned to the whole system. As you're using DFT its important to note that it will, in general, not result in proper charge dissociation. See e.g. J. Chem. Phys. 125, 194112 (2006); doi: 10.1063/1.2387954. -- --------------------------------------------------------------- Mr. Susi Lehtola, PhD Research Associate susi.lehtola++alumni.helsinki.fi Department of= Applied Physics http://www.helsinki.fi/~jzlehtol Aalto University Finland --------------------------------------------------------------- Susi Lehtola, FT Tutkijatohtori susi.lehtola++alumni.helsinki.fi Fysiikan lait= os http://www.helsinki.fi/~jzlehtol Aalto-yliopisto --------------------------------------------------------------- -=3D This is automatically added to each message by the mailing script =3D-=
or u= se:E-mail to administrators: CHEMISTRY-REQUEST[-]ccl.net or usehttp://www.ccl.net/chemistry/sub_unsub.shtml

As an additional point, t= he final charge distributions (if using appropriate theoretical methods) do= tend to follow basic chemical principles, so the bulk of the charge will end up on whichever species has the lowest ionization pote= ntial.

<= /p>

Sam

<= /p>

From: owner-ch= emistry+sabrash=3D=3Drichmond.edu-.-ccl.net [mailto:owner-chemistry+s= abrash=3D=3Drichmond.edu-.-ccl.net] On Behalf Of Mohan maruthi sena maruthi.sena/agmail.com
Sent: Monday, February 10, 2014 11:44 AM
To: Abrash, Samuel
Subject: CCL:G: How to consider charge on particular atom -lithium

Thank you very much f= or a reply,

Then instead of litiu= m ion, I have to give charge on the whole system. Will that be correc= t?

Thanks,

Mohan

On Mon, Feb 10, 2014 at 9:12 PM, Susi Lehtola susi.l= ehtola|a|alumni.helsinki.fi <<= a href=3D"mailto:owner-chemistry[-]ccl.net" target=3D"_blank">owner-chemist= ry[-]ccl.net> wrote:

Sent to CCL by: Susi Lehtola [susi.lehtola++alumni.helsinki.fi]
On Mon, 10 Feb 2014 20:28:54 +0530
"Mohan maruthi sena maruthi.sena[*]gmail.com" <owner-chemistry++ccl.net>
wrote:

> Hi all,
> I have a system which contains acet= one molecule and lithium ion.
> How can I specify that there is charge on the lithium ion in input fil= e for
> gaussian09. Is it enough if i mention at the beginning of the file &nb= sp;charge
> 1 and spin 1.

You can't assign elec= tronic charges to single atoms. Instead, the
distribution of charge is determined by the quantum mechanical
calculation, and different methods will result in different partial
charges on the atoms. The charge is assigned to the whole system.

As you're using DFT its important to note that it will, in general,
not result in proper charge dissociation. See e.g. J. Chem. Phys. 125,
194112 (2006); doi: 10.1063/1.2387954.
--
---------------------------------------------------------------
Mr. Susi Lehtola, PhD Research As= sociate
susi.lehtola++alumni.helsinki.fi Department of Applied Physics
http://www.h= elsinki.fi/~jzlehtol Aalto University
= ; Finland
---------------------------------------------------------------
Susi Lehtola, FT &n= bsp;Tutkijatohtori
susi.lehtola++alumni.helsinki.fi Fysiikan laitos
http://www.h= elsinki.fi/~jzlehtol Aalto-yliopisto
---------------------------------------------------------------

-=3D This is automatically added to each message by the mailing script =3D-= <br

E-mail to subscribers: CHEMISTRY[-]c= cl.net or use:
http://www.ccl.net/cgi-bin/ccl/send_ccl_message=

E-mail to administrators: CH= EMISTRY-REQUEST[-]ccl.net or use
http://www.ccl.net/cgi-bin/ccl/send_ccl_message=

Subscribe/Unsubscribe:
http://www.ccl.net/chemistry/sub_unsub.shtml

Before posting, check wait time at: http://www.ccl.net

Job: http://www.ccl.n= et/jobs
Conferences: http://server.ccl.net/chemistry/announcements/conferences/

Search Messages: http://www.ccl.net/chemistry/searchccl/index.shtml
<br
http://www.ccl.net/spammers.txt

RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/

--_000_A7C78D2AEE62DB40B9CB1ADE9D5990A2C2BFAB97quorrarichmonde_-- From owner-chemistry@ccl.net Mon Feb 10 16:29:00 2014 From: "Tymofii Nikolaienko tim_mail%a%ukr.net" To: CCL Subject: CCL:G: How to consider charge on particular atom -lithium Message-Id: <-49650-140210162517-23924-gMbwaR/kkwxAvQSw39PSgw=server.ccl.net> X-Original-From: "Tymofii Nikolaienko" Date: Mon, 10 Feb 2014 16:25:16 -0500 Sent to CCL by: "Tymofii Nikolaienko" [tim_mail**ukr.net] Dear Mohan, Dear colleagues! I'd like to slightly disagree with some answers given so far. It seems to me the correct way of translating of what we call a 'charge on the atomic ion' in the classical case into a language of quantum chemistry is a construction of the proper initial guess for molecular orbitals. Recall that all SCF (HF and DFT) methods begin with some initial guess for MOs and then improve this zero-th approximation iteratively by solving self-consistent-field equations. Unfortunately, I'm not aware of a quantum chemistry packages able to provide a convenient control over the initial guess generation (probably someone else does?). Perhaps, separating you system into fragments in Gaussian 09 and specifying the total charges of the fragments might be helpful (see http://www.gaussian.com/g_tech/g_ur/m_molspec.htm , see also a discussion on the "Fragment=N" at http://www.gaussian.com/g_tech/g_ur/k_guess.htm ) In addition to that, I'd like to pay the attention to NwChem package - see a paragraph on "CDFT -- Constrained DFT" at http://www.nwchem-sw.org/index.php/Density_Functional_Theory_for_Molecules They state there that " The constraint can be either on the charge or the spin density (# of alpha - beta electrons) with a user specified constaint value. ... To calculate the charge or spin density, the Becke, Mulliken, and Lowdin population schemes can be used. The Lowdin scheme is default while the Mulliken scheme is not recommended. " Hope this helps, Yours sincerely Tymofii 10.02.2014 18:15, S.Chandra Shekar chandrashekar[-]iisertvm.ac.in wrote: > Hi mohan, > > Yes. In your case it is sufficient to give charge to the whole system. it default assume the charge is on lithium. > > > On Mon, Feb 10, 2014 at 8:28 PM, Mohan maruthi sena maruthi.sena[*]gmail.com wrote: > > Hi all, > I have a system which contains acetone molecule and lithium ion. How can I specify that there is charge on the lithium ion in input file for gaussian09. Is it enough if i mention at the beginning of the file charge 1 and spin 1. > > %nprocshared=4 > %mem=4GB > %chk=peg_lico2 > # opt b3lyp/6-31+g(d,p) geom=connectivity > > optimization of the polyethylene glycol+lithium+carbondioxide > > 1 1 > > > > Thanks, > Mohan > > From owner-chemistry@ccl.net Mon Feb 10 17:03:00 2014 From: "Tymofii Nikolaienko tim_mail%x%ukr.net" To: CCL Subject: CCL:G: How to consider charge on particular atom -lithium Message-Id: <-49651-140210161533-23438-3zryq7rk0oc3Cgf8+qRnqA||server.ccl.net> X-Original-From: Tymofii Nikolaienko Content-Type: multipart/alternative; boundary="------------080003040802000100090603" Date: Mon, 10 Feb 2014 23:15:21 +0200 MIME-Version: 1.0 Sent to CCL by: Tymofii Nikolaienko [tim_mail],[ukr.net] This is a multi-part message in MIME format. --------------080003040802000100090603 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Dear Mohan, Dear colleagues! I'd like to slightly disagree with some answers given so far. It seems to me the correct way of translating of what we call a 'charge on the atomic ion' in the classical case into a language of quantum chemistry is a construction of the proper initial guess for molecular orbitals. Recall that all SCF (HF and DFT) methods begin with some initial guess for MOs and then improve this zero-th approximation iteratively by solving self-consistent-field equations. Unfortunately, I'm not aware of a quantum chemistry packages able to provide a convenient control over the initial guess generation (probably someone else does?). Perhaps, separating you system into fragments in Gaussian 09 and specifying the total charges of the fragments might be helpful (see http://www.gaussian.com/g_tech/g_ur/m_molspec.htm , see also a discussion on the "Fragment=N" at http://www.gaussian.com/g_tech/g_ur/k_guess.htm ) In addition to that, I'd like to pay the attention to NwChem package - see a paragraph on "CDFT -- Constrained DFT" at http://www.nwchem-sw.org/index.php/Density_Functional_Theory_for_Molecules They state there that " The constraint can be either on the charge or the spin density (# of alpha - beta electrons) with a user specified constaint value. ... To calculate the charge or spin density, the Becke, Mulliken, and Lowdin population schemes can be used. The Lowdin scheme is default while the Mulliken scheme is not recommended. " Hope this helps, Yours sincerely Tymofii 10.02.2014 18:15, S.Chandra Shekar chandrashekar[-]iisertvm.ac.in wrote: > Hi mohan, > > Yes. In your case it is sufficient to give charge to the whole system. > it default assume the charge is on lithium. > > > On Mon, Feb 10, 2014 at 8:28 PM, Mohan maruthi sena > maruthi.sena[*]gmail.com

> wrote: > > Hi all, > I have a system which contains acetone molecule and > lithium ion. How can I specify that there is charge on the lithium > ion in input file for gaussian09. Is it enough if i mention at the > beginning of the file charge 1 and spin 1. > > %nprocshared=4 > %mem=4GB > %chk=peg_lico2 > # opt b3lyp/6-31+g(d,p) geom=connectivity > > optimization of the polyethylene glycol+lithium+carbondioxide > > 1 1 > > > > Thanks, > Mohan > > --------------080003040802000100090603 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Dear Mohan, Dear colleagues!

I'd like to slightly disagree with some answers given so far.
It seems to me the correct way of translating of what we call a 'charge on the atomic ion' in the classical case
into a language of quantum chemistry is a construction of the proper initial guess for molecular orbitals.
Recall that all SCF (HF and DFT) methods begin with some initial guess for MOs and then improve
this zero-th approximation iteratively by solving self-consistent-field equations.
Unfortunately, I'm not aware of a quantum chemistry packages able to provide a convenient control
over the initial guess generation (probably someone else does?).
Perhaps, separating you system into fragments in Gaussian 09 and specifying the total charges of the fragments
might be helpful (see http://www.gaussian.com/g_tech/g_ur/m_molspec.htm , see also a discussion
on the "Fragment=N" at http://www.gaussian.com/g_tech/g_ur/k_guess.htm )
In addition to that, I'd like to pay the attention to NwChem package - see
a paragraph on "CDFT -- Constrained DFT" at http://www.nwchem-sw.org/index.php/Density_Functional_Theory_for_Molecules
They state there that "
The constraint can be either on the charge or the spin density (# of alpha - beta electrons) with a user specified constaint value. ...
To calculate the charge or spin density, the Becke, Mulliken, and Lowdin population schemes can be used.
The Lowdin scheme is default while the Mulliken scheme is not recommended. "

Hope this helps,
Yours sincerely
Tymofii

10.02.2014 18:15, S.Chandra Shekar chandrashekar[-]iisertvm.ac.in wrote:

Hi mohan,

Yes. In your case it is sufficient to give charge to the whole system. it default assume the charge is on lithium.

On Mon, Feb 10, 2014 at 8:28 PM, Mohan maruthi sena maruthi.sena[*]gmail.com <owner-chemistry() ccl.net> wrote:

Hi all,

I have a system which contains acetone molecule and lithium ion. How can I specify that there is charge on the lithium ion in input file for gaussian09. Is it enough if i mention at the beginning of the file charge 1 and spin 1.

%nprocshared=4
%mem=4GB
%chk=peg_lico2
# opt b3lyp/6-31+g(d,p) geom=connectivity

optimization of the polyethylene glycol+lithium+carbondioxide

1 1

Thanks,

Mohan

--------------080003040802000100090603-- From owner-chemistry@ccl.net Mon Feb 10 18:01:00 2014 From: "Susi Lehtola susi.lehtola.:.alumni.helsinki.fi" To: CCL Subject: CCL:G: How to consider charge on particular atom -lithium Message-Id: <-49652-140210175752-13977-lLDD5p21b5vedFt3UouwzA/a\server.ccl.net> X-Original-From: Susi Lehtola Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Date: Tue, 11 Feb 2014 00:57:44 +0200 MIME-Version: 1.0 Sent to CCL by: Susi Lehtola [susi.lehtola+*+alumni.helsinki.fi] On Mon, 10 Feb 2014 16:25:16 -0500 "Tymofii Nikolaienko tim_mail%a%ukr.net" wrote: > Sent to CCL by: "Tymofii Nikolaienko" [tim_mail**ukr.net] > Dear Mohan, Dear colleagues! > > I'd like to slightly disagree with some answers given so far. > It seems to me the correct way of translating of what we call a 'charge on the atomic ion' in the classical case > into a language of quantum chemistry is a construction of the proper initial guess for molecular orbitals. > Recall that all SCF (HF and DFT) methods begin with some initial guess for MOs and then improve > this zero-th approximation iteratively by solving self-consistent-field equations. What you anyway get out at the end is the converged density / molecular orbitals. In the ideal case these are independent of the used starting guess, but in reality convergence to saddle points or local minima may occur. At the end, what you will be interested in here is the partial charge on the lithium atom (within some partial charge determination scheme). Within standard DFT, you can't force it to be any integer number. Instead, the number will be fractional, and determined by the self-consistent iteration. Different model chemistries will give different fractional charges, and different partial charge schemes will also give different results for the same quantum mechanical wave function for the system. For example, let's say you were calculating LiF with a bond length of 1000 Å. Here, you essentially have free atoms. When you run the calculation, what your program will do is try to minimize the energy of the electronic system by changing the electron density. Here, the EA of F is larger than the IP of Li, and what you'll get is Li+ F-. > Unfortunately, I'm not aware of a quantum chemistry packages able to provide a convenient control > over the initial guess generation (probably someone else does?). > Perhaps, separating you system into fragments in Gaussian 09 and specifying the total charges of the fragments > might be helpful (see http://www.gaussian.com/g_tech/g_ur/m_molspec.htm , see also a discussion > on the "Fragment=N" at http://www.gaussian.com/g_tech/g_ur/k_guess.htm ) Practically all QC packages have multiple starting guesses implemented. A good guess is mainly important for faster convergence of the calculation; the most important is not to use a core guess for large systems, because the electrons will be much too compact. > To calculate the charge or spin density, the Becke, Mulliken, and Lowdin population schemes can be used. > The Lowdin scheme is default while the Mulliken scheme is not recommended. " In my experience the Löwdin scheme is much, much worse than Mulliken - In the Löwdin scheme, the deficiences of the Mulliken scheme are magnified. -- --------------------------------------------------------------- Mr. Susi Lehtola, PhD Research Associate susi.lehtola/a\alumni.helsinki.fi Department of Applied Physics http://www.helsinki.fi/~jzlehtol Aalto University Finland --------------------------------------------------------------- Susi Lehtola, FT Tutkijatohtori susi.lehtola/a\alumni.helsinki.fi Fysiikan laitos http://www.helsinki.fi/~jzlehtol Aalto-yliopisto --------------------------------------------------------------- From owner-chemistry@ccl.net Mon Feb 10 18:40:00 2014 From: "Jim Kress ccl_nospam_._kressworks.com" To: CCL Subject: CCL:G: How to consider charge on particular atom -lithium Message-Id: <-49653-140210183743-16422-cCM/JQtdGQSC6IW02YwPDg*_*server.ccl.net> X-Original-From: "Jim Kress" Content-Language: en-us Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="utf-8" Date: Mon, 10 Feb 2014 18:37:44 -0500 MIME-Version: 1.0 Sent to CCL by: "Jim Kress" [ccl_nospam,kressworks.com] AIM and NBO charges would be the best choice. Mulliken and Lowdin are far too basis set dependent. Jim -----Original Message----- > From: owner-chemistry+ccl_nospam==kressworks.com_-_ccl.net [mailto:owner-chemistry+ccl_nospam==kressworks.com_-_ccl.net] On Behalf Of Susi Lehtola susi.lehtola.:.alumni.helsinki.fi Sent: Monday, February 10, 2014 5:58 PM To: Kress, Jim Subject: CCL:G: How to consider charge on particular atom -lithium Sent to CCL by: Susi Lehtola [susi.lehtola+*+alumni.helsinki.fi] On Mon, 10 Feb 2014 16:25:16 -0500 "Tymofii Nikolaienko tim_mail%a%ukr.net" wrote: > Sent to CCL by: "Tymofii Nikolaienko" [tim_mail**ukr.net] Dear Mohan, > Dear colleagues! > > I'd like to slightly disagree with some answers given so far. > It seems to me the correct way of translating of what we call a > 'charge on the atomic ion' in the classical case into a language of quantum chemistry is a construction of the proper initial guess for molecular orbitals. > Recall that all SCF (HF and DFT) methods begin with some initial guess > for MOs and then improve this zero-th approximation iteratively by solving self-consistent-field equations. What you anyway get out at the end is the converged density / molecular orbitals. In the ideal case these are independent of the used starting guess, but in reality convergence to saddle points or local minima may occur. At the end, what you will be interested in here is the partial charge on the lithium atom (within some partial charge determination scheme). Within standard DFT, you can't force it to be any integer number. Instead, the number will be fractional, and determined by the self-consistent iteration. Different model chemistries will give different fractional charges, and different partial charge schemes will also give different results for the same quantum mechanical wave function for the system. For example, let's say you were calculating LiF with a bond length of 1000 Å. Here, you essentially have free atoms. When you run the calculation, what your program will do is try to minimize the energy of the electronic system by changing the electron density. Here, the EA of F is larger than the IP of Li, and what you'll get is Li+ F-. > Unfortunately, I'm not aware of a quantum chemistry packages able to > provide a convenient control over the initial guess generation (probably someone else does?). > Perhaps, separating you system into fragments in Gaussian 09 and > specifying the total charges of the fragments might be helpful (see > http://www.gaussian.com/g_tech/g_ur/m_molspec.htm , see also a > discussion on the "Fragment=N" at > http://www.gaussian.com/g_tech/g_ur/k_guess.htm ) Practically all QC packages have multiple starting guesses implemented. A good guess is mainly important for faster convergence of the calculation; the most important is not to use a core guess for large systems, because the electrons will be much too compact. > To calculate the charge or spin density, the Becke, Mulliken, and Lowdin population schemes can be used. > The Lowdin scheme is default while the Mulliken scheme is not recommended. " In my experience the Löwdin scheme is much, much worse than Mulliken - In the Löwdin scheme, the deficiences of the Mulliken scheme are magnified. -- --------------------------------------------------------------- Mr. Susi Lehtola, PhD Research Associate susi.lehtola#alumni.helsinki.fi Department of Applied Physics http://www.helsinki.fi/~jzlehtol Aalto University Finland --------------------------------------------------------------- Susi Lehtola, FT Tutkijatohtori susi.lehtola#alumni.helsinki.fi Fysiikan laitos http://www.helsinki.fi/~jzlehtol Aalto-yliopisto ---------------------------------------------------------------http://www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_unsub.shtmlhttp://www.ccl.net/spammers.txt