We present a simple derivation of the Hellmann–Feynman theorem at finite temperature. We
illustrate its validity by considering three relevant examples, which can be used in quantum …

The Kepler's third law is a relation between the period and the energy of two classical
particles interacting via a gravitational potential. Recent works showed that this law could be …

The eigensolutions of many-body quantum systems are always difficult to compute. The
envelope theory is a method to easily obtain approximate, but reliable, solutions in the case …

A uniform force like the weight has been shown to forbid Bose-Einstein condensation (BEC),
due to the discreteness of the Airy spectrum, resulting from the weight. We show that BEC is …

Abstract The Hellmann–Feynman, virial and comparison theorems are three fundamental
theorems of quantum mechanics. For the first two, counterparts exist for classical mechanics …

Most introductory books on quantum mechanics discuss the particle-in-a-box problem
through solutions of the Schrödinger equation, at least, in the one-dimensional case. When …