Explicit Consideration of Vibrational Anharmonicity in Molecular Crystals with Quantum-Mechanical Simulations

The vibrations of atoms within a crystalline lattice can give insight into properties of materials. In particular, vibrational anharmonicity is responsible for many critical phenomena, such as thermal effects, specifically in the low frequency range. While vibrational anharmonicity can be measured spectroscopically, quantum-mechanical simulations traditionally can not take anharmonicity into account. In this work, two recently developed methods, the VCI and VSCF models, are used to calculate the explicit anharmonicity in molecular crystals.