Subject: Re: CCL:semantics : molecular modelling

From: [email-masked] (Jeffrey L. Nauss)
Date: Tue, 17 Jun 1997 09:20:24 -0400

On Jun 16,  5:52pm, Alexandre Hocquet wrote:

> the words "molecular modelling" still appear confusing to me :

The question of the "proper" definition (if such a thing exists) for the
term "molecular modelling" is an interesting one and one that has
bothered me for some time as well.  So I will offer my thoughts on the
matter.

> While it seems logical to think that "molecular modelling" is that part
> of "computational chemistry" that describes behaviour of molecules by
>  the formalism of some theoretical model, there seems to exist in the
> community a much more restrictive use of "molecular modelling".
> This second definition could be "Use of any non quantum mechanics model
>  to describe the behaviour of molecules".

The immediate question that comes into my mind with Alexandre's
statement is: what is "computational chemistry?"  Why is there a
distinction between computational chemistry and molecular modelling?

I have resolved the issue in my own mind as follows.  Computational
chemistry would be the application of numerical calculations to the
study of molecular structure.  Thus I would include in that definition
ab initio, semi-empirical, AND empirical calculations.  On the other
hand, I consider molecular modelling to be a much more general term.
Molecular modelling would be the application of some form of a model to
studying molecular structure.  It would include computational chemistry
but also hand-held CPK models and simple drawings on paper.

Thus, as I explain in my molecular modelling lectures, Pauling's
discovery of the alpha helix was an example of molecular modelling.
All he did (according to legend, at least) was wrap a strip of paper
around a pencil.  Simple and primitive, yet it *was* a model of a
molecular.  Another classic example was the discovery of the DNA double
helix.  Using simple metal templates and rods, Watson and Crick
constructed a model of a molecule that answered many questions about
the properties of DNA.

Thus I consider computational chemistry to be a subset of the more
general field of molecular modelling.  Molecular modelling in itself may
not involve any computations.  But computational chemistry must.

I wonder if one could trace the initial usage of the terms.

-- 
  Jeffrey L. Nauss, PhD           Telephone: 513-556-0148          
  Dir. Molec. Model. Serv.        Fax:       513-556-9239
  Department of Chemistry         e-mail: [email-masked]    
  University of Cincinnati        URL http://www.che.uc.edu/~nauss