[Xplor-nih] Torsion angle dynamics

[Charles at Schwieters.org]

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Hello Lei--

>            I am writing to ask a very basic questions of torsion  
> angle dynamics. I am wondering how the equations of motion are  
> integrated in the simulation. My concern is the way to calculate the  
> derivative of the energy terms with respect to torsion angle. I read  
> some literature but not full understand all. Is it very convenient to  
> calculate this derivative when we already know the derivative of  
> energy with respect to the cartesian coordinates?
>            The reason I am asking is that I am using an external  
> potential in python. I only provide the way to calculate energy from  
> cartesian coordinates and the derivative of energy with respect to  
> cartesian coordinates. It really concerns me whether I am able to use  
> the IVM module correctly.

the IVM expects gradients with respect to cartesian atomic coordinates-
so I think you're calculating the correct quantity. Derivatives with
respect to torsion angles can be used within the IVM - internally, but i
have not yet made an external interface to these.

best regards--
Charles
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