# Re: [AMBER] CYM residue problem(MCPB)

From: FyD <fyd.q4md-forcefieldtools.org>
Date: Thu, 17 Oct 2013 20:53:19 +0200

Dear Houcemeddine,

I agree with Jason. Let's suppose your iron metal center is a a iron(III).

Fe has 26 electrons:
Fe 26 (8) [Ar].3d6.4s2 || | | | | ||
So Fe(III) has the following electron configuration:
Fe 26 (8) [Ar].3d5 | | | | |
-> this likely means a spin multiplicity = 5 single electrons + 1; i.e. 6

Now let's look at the total charge:
CYM is likely to have a total charge of -1
HID means a total charge of 0
(be sure that you have 3 HID - and neither HIE nor HIP;
if HIP the total charge = +1)

thus the total charge of "FeIII + CYM(-1) + 3 * HID(0)" = +2

You might be interested in using R.E.D. Server
http://q4md-forcefieldtools.org/REDS/ or better R.E.D. Server
Development (new charge models); the association of R.E.D. Python and
R.E.D. Server Development is in progress; I hope we will open that
soon...
The next step will be to propose to the community very powerful nodes
for R.E.D. Server Development/R.E.D. Python and user defined options
for QM computations...

regards, Francois

>> I try to parametrize a metal cluster containing 1 CYM residue and 3 others
>> HID. Until the steps of generating the input com files , all is working
>> perfectly, except when I run gaussian it always give the error: The
>> combination of multiplicity 1 and 219 electrons is impossible.
>
> I believe this problem is unrelated to your sidechain.bcl file. Your metal
> cluster has an odd number of electrons, yet in your Gaussian input file you
> claim that the multiplicity is 1. A multiplicity of 1 indicates that there
> are no spin-unpaired electrons. If you have an odd number of electrons,
> though, at least one of your spins must be unpaired, meaning that your
> multiplicity must be an even number (2 means 1 electron is unpaired, 4
> means 3 electrons are unpaired, etc.). It is important that you figure out
> what your spin multiplicity is and then adjust the Gaussian input file
> accordingly. Another thing to note is that you cannot use a restricted
> method (e.g., RHF) to compute a wavefunction or electron density. You need
> to use some method that can handle open-shell systems (e.g., ROHF or UHF).

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Received on Thu Oct 17 2013 - 12:00:03 PDT
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