Calculation of elastic constants in UC, US, and UTe

The calculated electronic structure and charge density of UC and US are reported. We also report calculations on the elastic constants of the cubic compounds UC, US, and UTe using the local-spin-density approximation (LSDA) to the exchange and correlation potential. Good agreement between calculations and experiment has been obtained for UC and US suggesting that the chemical bonding is well reproduced by LSDA for these two compounds. In contrast, for UTe the calculations do not reproduce the measured negative Poissons ratio (negative ${\mathit{C}}_{12}$). We suggest that the failure to describe the elasticity of UTe reflects the weakness of LSDA in describing accurately electron systems that are strongly correlated and we speculate that UTe is an anomalous, possibly mixed valent, system.