**Quantifying contributions to the entropy of melting**

As temperature increases, atomic scale disorder, or entropy, drives the thermophysical properties of materials. One way it does this is by passing heat through materials in the form of vibrations. In solids, these vibrations are called phonons, and their behaviors are used to predict macroscopic properties such as thermal expansion and thermal conductivity. Other forms of entropy include configurational and electronic entropy, which also evolve with temperature. Configurational changes in solids are often small, but in liquids, the prominence of diffusion makes this contribution significant. This dissertation presentation addresses these atomistic components of entropy in the melting of monatomic systems using inelastic neutron scattering experiments and supporting computations. In the six elements studied, Ge, Si, Bi, Sn, Pb, and Li, it was found that if the change in vibrational entropy across melting, ΔSvib, is zero, the total entropy of fusion corresponds to a value of 1.2kB/atom, approximately the value of the empirical “Richard’s rule”. Elements having values of ΔSfus that depart from this value of Richard’s rule have both an additional ΔSvib and an additional ΔSconfig. Surprisingly, the extra ΔSconfig is close to 80% of ΔSvib, for both positive and negative deviations from Richard’s rule. This implies a correlation between the change in the number of basins in a potential energy landscape and the change in the inverse of their curvature upon melting.

**About the QSQM:** The EFRC-QSQM center aims to develop and apply nontrivial quantum sensing to measure and correlate local and nonlocal quantum observables in exotic superconductors, topological crystalline insulators, and strange metals. The center is led by the University of Illinois at Urbana-Champaign in partnership with the University of Illinois at Chicago and the SLAC National Accelerator Laboratory.