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

From: houcemeddine <hothman.pasteur.fr>
Date: Fri, 18 Oct 2013 15:11:14 +0200

Thanks Jason and François,
The multiplicity is indeed relevant for the computation. The problem was
solved when adjusting the multiplicity to +2.

Best regards

On 10/17/2013 08:53 PM, FyD wrote:
> 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 Fri Oct 18 2013 - 06:30:05 PDT
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