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I found this on Google Books: http://books.google.dk/books?id=v5v...resnum=5&ved=0CCwQ6AEwBA#v=onepage&q=&f=false

Here they say that whenever we write the Hamiltonian for a non-interacting system in its eigenbasis, then we have that

[tex]

A(\nu, \omega) = 2\pi \delta(\omega-\varepsilon_\nu).

[/tex]

How can this statement be proven? Do you have any hints for this?

Any help will be greatly appreciated.

Sincerely,

Niles.

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# Greens functions and density of states

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