Polyakov, E., & Vorontsov-Velyaminov, P. (2007). A quantum gas in an external field at finite temperatures. An exact expression for density and exited states. Numerical Methods and Programming (Vychislitel’nye Metody I Programmirovanie), 8(14), 334–351. Retrieved from https://en.num-meth.ru/index.php/journal/article/view/275