Comparison of a quantum random number generator with pseudorandom number generators for their use in molecular Monte Carlo simulations Abstract: Four pseudorandom number generators were compared with a physical, quantum-based random number generator using the NIST suite of statistical tests, which only the quantum-based random number generator could successfully pass. We then mea-sured the effect of the five random number generators on various calculated properties in different Markov-chain Monte Carlo simulations. Two types of systems were tested: conformational sampling of a small molecule in aqueous solution and liquid methanol under constant temperature and pressure. The results show that poor quality pseu-dorandom number generators produce results that deviate significantly from those obtained with the quantum-based random number generator, particularly in the case of the small molecule in aqueous solution setup. In contrast, the widely used Mersenne-Twister pseudorandom generator and a 64-bit Linear Congruential Generator with ascrambler produce results that are statistically indistinguishable from those obtained with the quantum-based random number generator.