~~NOTOC~~
====== Examples : Pair Potentials ======

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//**Warning:**//
This is an example potential. Please do NOT use it for any real simulations!
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This is a simple pair potential that can be used in //potfit//. 
The analytic function used is a Lennard-Jones.

It makes use of the **fixing parameters** feature.

<code potfit Example_Pair_5>
#F 0 3
#T PAIR
#I 0 0 0
#E

type lj
cutoff 6.0
# The following parameter is fixed
epsilon 0.10    0.00    0.00
sigma   2.50    1.00    4.00

type lj
cutoff 6.0
# The following parameter is fixed
epsilon 0.10    0.10    0.10
sigma   2.50    1.00    4.00

type lj
cutoff 6.0
# The following parameter is fixed
epsilon 0.10    1.00    1.00
sigma   2.50    1.00    4.00
</code>

The optimization of single parameters can be disabled with this feature. The parameter will be removed from
the optimization table and remain at its initial value. For all three lj-potentials in the above
example the epsilon parameter will not be optimized, it will always have the fixed value of 0.1.
To fix a parameter, the lower and upper bound have to be equal.

==== makeapot ====

The example potential can be generated with the following ''makeapot'' command:

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//**Hint:**//
The parameters have to be fixed manually in the potential file!
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  makeapot -n 2 -i pair -f 3*lj