CALCULATION OF ELASTIC-CONSTANTS IN UC, US, AND UTE

The calculated electronic structure and charge density of UC and US ar e reported. We also report calculations on the elastic constants of th e cubic compounds UC, US, and UTe using the local-spin-density approxi mation (LSDA) to the exchange and correlation potential. Good agreemen t between calculations and experiment has been obtained for UC and US suggesting that the chemical bonding is well reproduced by LSDA for th ese two compounds. In contrast, for UTe the calculations do not reprod uce the measured negative Poissons ratio (negative C-12). We suggest t hat the failure to describe the elasticity of UTe reflects the weaknes s of LSDA in describing accurately electron systems that are strongly correlated and we speculate that UTe is an anomalous, possibly mixed v alent, system.