[ghemical-devel] no ESP-colored WDW-surface if CHARGE<>1

[Tommi Hassinen]

On Tue, 19 Mar 2002, Radek Liboska PhD. wrote:

> Hi,
> 
> no ESP-colored WDW-surface if CHARGE<>1 ??
> MM and QM mode, both.
> 
> Tested on several anions and cations (CH3O-,....)
> 
> Regards
>   Radek

Hi!

Let's see the both cases:

In MM, the problems relate to the rather poor forcefield and it's
parameters. Ideally, the program should detect the ionic groups and assign
formal charges: +1 or whatever. In the second stage, these formal charges
are smoothed a bit to give "partial atomic charges". Unfortunately, the
formal charges detection doesn't work at the moment (that's why I have
described the forcefield as "experimental" and "untested" and only
recommended it for organic molecules). I have been working for better
parameter sets and I will start adding them immediately when they are
better than the current set.

In QM, I think the situation is better. Before starting the calculations,
you have to go in "Compute/Setup" in the popup menu, and set the total
charge of the system. I think it works, except that vdW-plots look odd
since they are badly scaled (pos/neg potential dominates and the plots are
single-coloured). But if you look at an ion pair (with total charge = 0):

            +       -
        CH3-NH3     COO-CH3

It seems to work fine and you probably see the origin of this "scaling
problem" more easily.

At the moment I don't know any criteria how to scale the colours for ionic
systems (that is, for which potential value we give the green colour,
instead of the current 0.0).

	Tommi