Re: [ESPResSo] Subsection 5.2.1 ESPResSo User's Guide

[Olaf Lenz]

Hello!

Ahmad A. J. Agung wrote:
> based on these lines, my questions are:
> 1. If r = r_{off} + \sigma, how could the potential (V_{LJ}(r)) 
become \epsilon(1 + c_{shift})?. Since if we put the r value to eq. 
(5.1), the potential will equal to 4 \epsilon c_{shift}.

> 2. In my expectation, attractive interaction will occur after 
molecules distance beyond r = r_{off} + 2^{fract{1}{6}}\sigma, as the 
force become (-). But these line mentioned "The attractive parts starts 
beyond r = r_{off} + \sqrt[6]{sigma}", do I miss something?.

Indeed you have found two errors in the User's Guide. I have fixed it, 
and it will occur in future versions, including thanks to you!

The minimum of the LJ potential is of course at r = r_{off} + 
2^{fract{1}{6}}\sigma!
I think what the original author wanted to say is that 
V_LJ(r_{off}+2^(1/6)*\sigma) = -\epsilon + 4 \epsilon c_{shift}. This 
confusion is caused by the two competing definitions of the LJ potential.

> Does anyone can help me recover my confusion? Since I am new and very 
inexperianced in this area.

For being inexperienced in the area, you asked exactly the right 
questions. So: thanks for the questions!

Olaf