[Pw_forum] what is alphamix(niter)

Paolo Giannozzi giannozz at nest.sns.it
Thu Feb 24 16:27:03 CET 2005

On Thursday 24 February 2005 14:33, aaron at chips.ncsu.edu wrote:

> From the Doc files:
>  alpha_mix(niter) mixing factor (for each iteration) for alpha_mix(1)=0.7
>                   vnew(in) = alpha_mix*vold(out) + (1-alpha_mix)*vold(in)

actually it is more complex than this. The above is "simple mixing",
but what the phonon code uses is a more sophisticated "Broyden 
mixing": D.D.Johnson, PRB 38, 12807 (1988). The meaning of alpha_mix 
is anyway the same: how much of the output potential is added to the
input potential for the next iteration.

> the integer in parentheses is the iteration number for which you wish
> to set the alpha_mix.

this is a possibility that was added years ago for some cases of
difficult convergence. It may be ignored: just set alpha_mix(1)
to the desired value for all iterations


Paolo Giannozzi             e-mail:  giannozz at nest.sns.it
Scuola Normale Superiore    Phone:   +39/050-509876, Fax:-563513 
Piazza dei Cavalieri 7      I-56126 Pisa, Italy

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