Debra Bernhardt (nee Searles) is a world leader in nonequilibrium statistical mechanics. She is widely known for the first rigorous derivation of a fluctuation relation, known as the Evans–Searles Fluctuation Theorem, showing the second law of thermodynamics can be derived mathematically rather than just postulated as a law of nature. The theorem has broad implications for the behaviour of small systems where fluctuations become pronounced. Debra has also made significant contributions to theoretical computational chemistry, including combining quantum chemistry and molecular simulation, as well as the calculation of transport properties of materials.