Hi Lin Xiao, The f-sum rule says the integrated oscillator strength should be equal to the number of electrons. In siesta, the number of available unoccupied states is limited by the size of the basis set. Increase DZP to TZP or TZDP, and the f-sum should improve.
Cheers, Marty On 18 January 2011 07:39, lin xiao <[email protected]> wrote: > Dears, > When i use optical module,it always shows this warning: > *[yangxu@WimaxServer 20110113-10]$ /opt/siesta-3.0-rc2/bin/input < > Graphene-optical.EPSIMG* > * ## 0.000000000000000E+000 19.9999000000000 * > * ## 1* > * ## 0.661800000000000 * > * ## 0.000000000000000E+000* > *Fsum rule is not fulfilled by more than a 20%* > * The dielectric function will be extended* > * to higher energies by enforcing the Fsum rule* > * This will increase the quality of the quantities* > * calculated via the Kramers-Kroning relation* > and here is the explanation of fsum-rule in the optical module: > If the F-sum rule is not fulfilled by an amount larger than > certain percentage specified in the program via the parameter THRESHOLD, the > imaginary part of the dielectric function will be appendedby a tail of the > form: > C/w**p > where C and p are determine to ensure continuity and to enforce the F-sum > rule.This should increase the quality of the quantities determined via > theKramers-Kroning relations, however it is not very sophisticated and in > certaincases it can create pathological problems. Anyway, it can be > easily desactivated by setting THRESHOLD to zero. > What should i do to fulfill the f-sum rule? > Should i reset my parameters in the '.fdf' file(see in the attachment) ? > > I am looking forward! > THX! > xiaolin,from ZJU > * > * > * > * > >
