Learn the fundamental concepts of stress, enthalpy, and variable cell optimization in computational materials science through this 59-minute lecture by Stefano de Gironcoli from Materials Cloud. Explore the theoretical foundations of stress tensors in crystalline systems and understand how enthalpy calculations relate to structural optimization problems. Discover the mathematical framework behind variable cell optimization techniques used in density functional theory calculations. Examine the relationship between stress and forces in periodic systems, and gain insights into how these concepts apply to predicting equilibrium crystal structures and phase transitions in materials.