CCL:G: Question on calculation of charge center of electrons in a
molecule
- From: John McKelvey <jmmckel .. gmail.com>
- Subject: CCL:G: Question on calculation of charge center of
electrons in a molecule
- Date: Mon, 29 Nov 2010 12:29:28 -0500
Sent to CCL by: John McKelvey [jmmckel++gmail.com]
On the other hand the NBO program can compute ZDO type charges which
are atom-centered and are along the diagonal of the density matrix and
for which the sum is the same as the number of electrons in the
system.
John McKelvey
On Mon, Nov 29, 2010 at 10:01 AM, James Eilers jeilers!^!siue.edu
<owner-chemistry###ccl.net> wrote:
> Mulliken charges also include the "shared" electron density or
cross terms
> between atomic orbitals on different centers.
>
> On Nov 27, 2010, at 8:02 PM, Jiabo Li jiaboli/./yahoo.com wrote:
>
>> To understand what is wrong, you can look at a simple example: the
>> hydrogen atom in its excited state with the single electron on a SP
hydride
>> orbital. In this case, the electron density is not central symmetric
but
>> polarized, and the dipole moment is not zero (a big dipole moment),
while in
>> this case the net atomic charge is zero (neutral).
>>
>> Jiabo
>>
>> --- On Fri, 11/26/10, Herbert Fruchtl
herbert.fruchtl[#]st-andrews.ac.uk
>> <owner-chemistry]*[ccl.net> wrote:
>>
>>
>>> From: Herbert Fruchtl herbert.fruchtl[#]st-andrews.ac.uk
>>> <owner-chemistry]*[ccl.net>
>>
>> Subject: CCL:G: Question on calculation of charge center of electrons
in a
>> molecule
>> To: "Li, Jiabo " <jiaboli]*[yahoo.com>
>> Date: Friday, November 26, 2010, 6:25 AM
>>
>>
>>
>> Sent to CCL by: Herbert Fruchtl [herbert.fruchtl::st-andrews.ac.uk]
>> The centre of charge of each Gaussian function is its origin, i.e. the
>> nucleus if you have atom-centred basis functions. The Mulliken charge
is the
>> sum of those functions, multiplied with their occupation number.
Shouldn't
>> this sum have its centre on the nucleus as well? And the sum of all of
them
>> (over all atoms) gives the complete charge distribution. Where am I
going
>> wrong?
>>
>> Herbert
>>
>> Ulf Ekström ulfek(~)few.vu.nl wrote:
>>>
>>> Sent to CCL by: =?ISO-8859-1?Q?Ulf_Ekstr=F6m?= [ulfek],[few.vu.nl]
>>> On Thu, Nov 25, 2010 at 9:56 AM, Herbert Fruchtl
>>> herbert.fruchtl-.-st-andrews.ac.uk <owner-chemistry .
ccl.net> wrote:
>>>>
>>>> Sent to CCL by: Herbert Fruchtl
[herbert.fruchtl*_*st-andrews.ac.uk]
>>>> I don't have time to look at the maths of it, but I think the
centre of
>>>> charge of the electron density should be identical to the
centre of the
>>>> Mulliken charges, which would be easy to calculate (analogous
to the
>>>> centre
>>>> of mass).
>>>
>>> This will not work, for example if you have a single centre basis
set all
>>> Mulliken charge would be on that center. What you should do is to
compute
>>> the dipole moment of the molecule and use that to work out the
center
>>> of charge.
>>>
>>> Sincerely,
>>> Ulf Ekstrom>
>>
>> -- Herbert Fruchtl
>> Senior Scientific Computing Officer
>> School of Chemistry, School of Mathematics and Statistics
>> University of St Andrews
>> --
>> The University of St Andrews is a charity registered in Scotland:
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>>
>> <table cellspacing="0" cellpadding="0"
border="0" ><tr><td valign="top"
>> style="font: inherit;"><DIV>To understand what is
wrong, you can look at a
>> simple example: the hydrogen atom in its excited state with the single
>> electron on a SP hydride orbital. In this case, the electron density is
not
>> central symmetric but polarized, and the dipole moment is not zero (a
big
>> dipole moment), while in this case the net atomic charge is zero
>> (neutral).</DIV>
>> <DIV> </DIV>
>> <DIV>Jiabo<BR><BR>--- On <B>Fri, 11/26/10,
Herbert Fruchtl
>> herbert.fruchtl[#]st-andrews.ac.uk
>> <I><owner-chemistry]*[ccl.net></I></B>
wrote:<BR></DIV>
>> <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px;
BORDER-LEFT:
>> rgb(16,16,255) 2px solid"><BR>From: Herbert Fruchtl
>> herbert.fruchtl[#]st-andrews.ac.uk
>> <owner-chemistry]*[ccl.net><BR>Subject: CCL:G:
Question on calculation
>> of charge center of electrons in a molecule<BR>To: "Li,
Jiabo "
>> <jiaboli]*[yahoo.com><BR>Date: Friday, November 26,
2010, 6:25
>> AM<BR><BR>
>> <DIV class=plainMail><BR>Sent to CCL by: Herbert Fruchtl
>> [herbert.fruchtl::st-andrews.ac.uk]<BR>The centre of charge of
each Gaussian
>> function is its origin, i.e. the nucleus if you have atom-centred basis
>> functions. The Mulliken charge is the sum of those functions,
multiplied
>> with their occupation number. Shouldn't this sum have its centre on the
>> nucleus as well? And the sum of all of them (over all atoms) gives the
>> complete charge distribution. Where am I going
wrong?<BR><BR>
>> Herbert<BR><BR>Ulf Ekström ulfek(~)few.vu.nl
wrote:<BR>> Sent to CCL by:
>> =?ISO-8859-1?Q?Ulf_Ekstr=F6m?= [ulfek],[few.vu.nl]<BR>> On
Thu, Nov 25,
>> 2010 at 9:56 AM, Herbert Fruchtl<BR>>
herbert.fruchtl-.-st-andrews.ac.uk
>> <owner-chemistry . ccl.net>
wrote:<BR>>> Sent to CCL by: Herbert
>> Fruchtl [herbert.fruchtl*_*st-andrews.ac.uk]<BR>>>
I don't have time
>> to look at the maths of it, but I think the centre
of<BR>>> charge of
>> the electron density
>> should be identical to the centre of
the<BR>>> Mulliken charges,
>> which would be easy to calculate (analogous to the
centre<BR>>> of
>> mass).<BR>> <BR>> This will not work, for
example if you have a single
>> centre basis set all<BR>> Mulliken charge would be on that
center. What
>> you should do is to compute<BR>> the dipole moment of the
molecule and
>> use that to work out the center<BR>> of
charge.<BR>> <BR>>
>> Sincerely,<BR>> Ulf Ekstrom> <BR><BR>--
Herbert Fruchtl<BR>Senior
>> Scientific Computing Officer<BR>School of Chemistry, School of
Mathematics
>> and Statistics<BR>University of St
Andrews<BR>--<BR>The University of St
>> Andrews is a charity registered in Scotland:<BR>No
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>
> James E. Eilers
> Professor
> Chemistry Department
> Southern Illinois University Edwardsville
> (618)650-3559
>
--
John McKelvey
10819 Middleford Pl
Ft Wayne, IN 46818
260-489-2160
jmmckel###gmail.com