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Ebert - Psi-k

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Ludwig<br />

Maximilians-<br />

Universität<br />

München<br />

Spectral representation of G(⃗r, ⃗r ′ , E)<br />

ψ i (⃗r, E i ) complete and orthogonal set of eigenfuctions<br />

(E i − H) ψ i (⃗r, E i ) = 0<br />

(E − H) G(⃗r, ⃗r ′ , E) = δ(⃗r − ⃗r ′ )<br />

G(⃗r, ⃗r ′ , E) for fixed ⃗r ′ and E can be expanded into a<br />

series of ψ i (⃗r, E i ) (Mercer’s theorem)<br />

∑<br />

G + (⃗r, ⃗r ′ , E) = lim<br />

ɛ→0<br />

retarded Green’s function<br />

i<br />

ψ i (⃗r)ψ × i (⃗r ′ )<br />

E − E i + iɛ<br />

poles of G + (⃗r, ⃗r ′ , E) indicate eigenvalues<br />

lim ɛ→0 avoids divergencies<br />

NB: × is in general equivalent to †<br />

KKR07 – p.8/100

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