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Re^3: Particle energy is less than sum of components energies

Andrei V Scherbinin
andrei.scherb@gmail.com


Hello,

Now it seems more clear for me.

1. Your negatively charged complex is probably not able to bind as many M+ cations as you wish
for simple electrostatic reasons. For example, in ionic crystalline  solid, the coordination sphere
may include a lot of counter-ions just because of presence of the Madelung potential of the surrounding lattice. So if your aim is to simulate the condensed phase, you should provide adequate environoment, otherwise it makes little sense.

2. You use local optimization routines which do not guarantee that you reach the global minimum.
Moreover, there are no numerical methods allowing to do this with a guarantee. So if you still
suspect that the problem is in the algorithms you use, you could examine a kind of multi-start
methodology, i.e., perform a number of local optimization runs starting with different initial
structures generated manually or randomly.

However, I think that the real problem is 1. rather than 2.

Best wishes,

Andrei



On Thu Apr 22 '10 4:27pm, Vyacheslav wrote
------------------------------------------
>Hi!
>Dear Andrei, sorry for the incorrect formulation of my question. I mean that at some number of M+ cations I obtain (sometimes) the system which absolute value of energy is less, than the total energy of initial particles. That is, the final system is non-stable relatively initial particles.
>   As it seems to me, the ideal algorithm of local minimum search should not find such structures. However, as it finds them, I am compelled to compare energy of final system to energy of initial system in each doubtful calculation.
>   In this connection I wanted to ask, whether there are any FF options which allow reducing probability of similar systems finding?
>Thanks!
>Vyacheslav

>-------------------------------------------------
>On Wed Apr 21 '10 10:18pm, Andrei V Scherbinin wrote
>----------------------------------------------------
>>Hello Vyacheslav,

>>Sorry to say, I didn't understand the problem rised in your question.

>>Do you mean that adding counter-ions stabilizes your original charged complex?
>>Or what did you mean when saying:  

>>>I receive systems which energy is less than sum of initial particles energies.
>>
>>
>>
>>


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