The structure and electric field gradients at the site with a histidine, an aspartic acid, a cysteine, and 1-2 water molecules as ligands are investigated with density functional and Hartree-Fock methods. This site has been shown experimentally to be occupied in the mononuclear cadmium-beta-lactamase. Three types of model systems are studied: (1) the metal ion and the coordinating ligands, (2) the metal ion, the coordinating ligands and the local hydrogen-bonding network, and (3) the metal ion, the coordinating ligands, the hydrogen-bonding network, and the constraints from the surrounding protein. Good agreement with experimental data is obtained when optimizing systems 2 and 3, indicating that inclusion of the hydrogen-bonding network is important. The results suggest that the site is five-coordinated and structurally flexible.