Subject: Summary on modeling corrosion inhibitors

From: "Danya Yang" <[email-masked]>
Date: Mon, 15 Aug 94 22:11:06 MDT

Many thanks to those who replied to my query about modeling corrosion 
inhibitors.  I've got three replies, and they are all very helpful indeed.  
Here are my original question and the replies I've got:

My original query was:

> Dear Netters,
>
> I am planning to do some modeling work on corrosion inhibitors (organic 
> compounds) by studying adsorption behavior of a molecular layer at the
> metal-solution interface.  I am looking for a visualization software which 
> can show how those organic molecules pack together (to form a molecular 
> layer) on a metal surface, and how the molecular layer interacts with the 
> metal surface, or a software which models adsorption phenomenon ( physical 
> or chemical ).
> 
> I appreciate any suggestions from you regarding to the softwares or published
> papers in this field. I'll summarize the replies if there is enough interest.
> 
> 

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Message 1: from Craig W. Burkhart ([email-masked])

Message-Id: <9408041310.AA12996@rds325>
To: "Danya Yang" <[email-masked]>
Subject: Re:  CCL:any software for corrosion inhibitors

I read with interest your desire to model metal-solution interfaces.

As far as the visualization is concerned, just about any of the commercial
packages from MSI, Biosym or Tripos will do. AVS from DASGroup would also
probably work for these calculations.

More importantly, I will pose to you, what methods are you going to use
in this study? Using quantum chemical approaches will be tedious and prone
to errors in judgment. Using molecular mechanics is okay, but you better
be sure that the parameterizations are good--otherwise you will get garbage.

My advice is to find a good molecular mechanics forcefield to get a
physical feel for the problem. By "good forcefield" I mean that it is
well-parameterized for your group of elements in this application. Then,
after you've done the "cheap" calculations, do the quantum chemistry on
small clusters. The metals-organics problem is one that has been around
for some time now, and has had some small successes. My guess is that
you will have to borrow some of the techniques from the solid-state
physics folks (viz., metal pseudopotentials for the quantum chemistry)
to make the problem tractable for modestly sized metal surfaces.
>From the molecular statistical mechanics standpoint, you will need
to examine the various methods of computing interfacial adsorption
isotherms. Computing Langmuir, etc., isotherms can be readily done
using molecular dynamics, but like the quantum chemistry, is frought
with the quality of the parameterization (that is, the applicability
of the forcefield) and size limitations dictated by your hardware.

Btw, don't forget that you will also have to master techniques to
generate the metal surface. The most obvious, and most difficult
(but also the most realistic), technique to generate an amorphous
oxide surface (because you WILL have to take a look at them--clean
metal surfaces are probably not meaningful. Almost all metals,
except for the noble metals, will form an instantaneous oxide surface)
is to use stochastic (Monte Carlo) methods of modelbuilding.
Juan de Pablo's research group at Wisconsin may be able to help
you there. The generation of a meaningful metal oxide surface
is almost a research project in itself.

>From a practical standpoint, Tom Fabish of Alcoa ([email-masked])
has done many of these things in the past. You may want to contact him
(yes, you can tell him I foisted you upon him :-) ), as he can probably
help you avoid some of the many landmines that await you.

Good luck. If I can be of any further surface, just give me an e-jingle...

--------------------------------------------------------------------------
Craig W. Burkhart, Ph.D.                   Senior Research Chemist 
E-mail: [email-masked]             The Goodyear Tire & Rubber Co.
Fone:   216.796.3163                       Research Center
Fax:    216.796.3304                       142 Goodyear Boulevard
					   Akron, OH   44305

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Message 2: from John Meehan <[email-masked]>

Subject: Re: CCL:any software for corrosion inhibitors
In-Reply-To: <[email-masked]>
Message-Id: <[email-masked]>

We are currently working with C.S.(Steven) Sikes (Uni. Soth Alabama) on
very similar aspects of inhibition of crystallization. We are primarily
looking at Calcium oxalates, carbonates etc but are also interested in
scale and corrosion.

The procedure we have used is to
1) Grow crystals in the presence or absence of inhibitor
2) Examine the morphology using SEM and light microscopy to determine
which crystl plane the inhibitor has its primary mode of action 
3) Examine the crystal using Atomic force microscopy at the molecular
level to actually SEE deformations in the surface (not yet....but we will!!)
4) Model the interaction

Step 4 is performed after optimization of the structures using basic ab
initio or semi-empirical methods, and with appropriate charge fitting from
known physical measurements. The whole lot is then used in the Quanta
package with the Charmm forcefield to allow "docking" of the inhibitor
with the surface. 

To date, the results have been excellent!!!!!!!

I hope this helps......please post me a copy of your summary :-)

Cheers
John

----------------------------------------------
John Meehan                   O     CH2-COOH      
Department of Biochemistry    "    /
University of Tasmania,    HO-P-O-C-COOH
Australia                     |    \
                             HO     CH2-COOH
PHOSPHOCITRIC ACID ----    A powerful, natural 
   inhibitor of Pathological Biomineralization
----------------------------------------------

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Message 3: from Beverly Bendiksen <[email-masked]>

Subject: Re: CCL:any software for corrosion inhibitors
To: Danya Yang <[email-masked]>
In-Reply-To: <[email-masked]>
Message-Id: <[email-masked]>
 
Dear Danya - 

Sorry for the delayed reply to your posting, but I've been out of the 
country for a while.

I've done some modeling of corrosion  inhibitors, and found that Cerius2 
distributed by Molecular Simulations is an excellent package for this 
type of system.  It has a very good crystal builder and variety of 
forcefields and parameters to choose from.  

Getting software to visualize inhibitor interactions on the surface is actually
quite easy, the difficulty is defining the corrosion inhibition model.  I've 
used metal oxides instead of the pure metal as the substrate, since I think 
this better represents the surface in an aqueous system.

Happy computing!

Beverly Bendiksen  [email-masked]
Pittsburgh, PA

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Thanks again, Craig, John and Beverly.

Danya