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The friction coefficient is defined as the integral over
the memory function. In the discrete case we write
 |
(4.96) |
As shown in [57], the AR model allows us to express
as
 |
(4.97) |
where the coefficients
are given by eq. (4.76), and the roots
must fulfill the stability
criterion (4.77).
Inserting (4.97) into (4.81) yields
, the z-transform of the discrete memory
function within the AR model,
 |
(4.98) |
Using (4.98) we obtain thus within the AR model
 |
(4.99) |
This shows that
can be obtained from the zeros
of the characteristic polynomial
, defined in (4.74).
In the framework of the autoregressive model, nMOLDYN allows one to calculate the VACF, the VACF memory function, the
DOS, the MSD, and the AR coefficients
of the velocity trajectory, averaged over all selected atoms
and three Cartesian coordinates.
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pellegrini eric
2009-10-06