Kato, T.: Schrödinger operators with singular potentials. Israel J. Math.13, 135–148 (1972)
Povzner, A.Ya.: The expansion of arbitrary functions in terms of eigenfunctions of the operator−Δu+cu. Amer. Math. Soc. Transl., II. Ser.60, 1–49 (1967) (english translation of Mat. Sbornik, n. Ser.32, 109–156 (1953))
Reed, M., Simon, B.: Methods of modern mathematical physics II: Fourier analysis, self-adjointness. New York, San Francisco, London: Academic Press 1975
Rellich, F.: Halbbeschränkte Differentialoperatoren höherer Ordnung. In: Proceedings of the International Congress of Mathematicians (Amsterdam 1954), Vol.3, pp. 243–250. Groningen-Amsterdam: Noordhoff, North-Holland 1956
Simader, C.G.: Bemerkungen über Schrödinger-Operatoren mit stark singulären Potentialen. Math. Z.138, 53–70 (1974)
Simon, B.: Essential self-adjointness of Schrödinger operators with positive potentials. Math. Ann.201, 211–220 (1973)
Stetkaer-Hansen, H.: A generalization of a theorem of Wienholtz concerning essential selfadjointness of singular elliptic operators. Math. Scandinav.19, 108–112 (1966)
Walter, J.: Note on a paper by Stetkaer-Hansen concerning essential selfadjointness of Schrödinger operators. Math. Scandinav.25, 94–96 (1969)
Wienholtz, E.: Halbbeschränkte partielle Differentialoperatoren zweiter Ordnung vom elliptischen Typus. Math. Ann.135, 50–80 (1958)