Response functions and Green’s functions
Response functions are the bread and butter of theoretical physics and the connection to important experimental measurements. The basic formulas are rooted in well-known perturbation expressions given in Ch. 3. This appendix is devoted to characteristic forms and properties of response functions, sum rules, and Kramers-Kronig relations. The most important example is the dielectric function described in App. E. Useful expressions are given for self-consistent field methods, which leads to “RPA” and other formulas needed in Chs. 5, 19, and 20.
D.1 Static response functions
Static response functions play two important roles in electronic structure. One is the calculation of quantities ...