1. Avron, J., Herbst, I., Simon, B.: Schrödinger operators with magnetic fields. I. General interactions. Duke Math. J. 45, 847–883 (1978)
2. Behrndt, J., Gesztesy, F., Nakamura, S.: Spectral shift functions and Dirichlet-to-Neumann maps. Math. Ann. 371, 1255–1300 (2018)
3. Birman, M.Š.: Perturbations of the continuous spectrum of a singular elliptic operator by varying the boundary and the boundary conditions, (Russian) Vestnik Leningrad. Univ. 17(1), 22-55 (1962)
4. English translation in: Spectral theory of differential operators, 19-53, Amer. Math. Soc. Transl. Ser. 2, 225, Adv. Math. Sci., 62, Amer. Math. Soc., Providence, RI (2008)
5. Birman, M.Š., Kreĭn, M.G.: On the theory of wave operators and scattering operators. Dokl. Akad. Nauk SSSR 144, 475-478 (1962) (Russian)