Electronic band gaps and dielectric constants are obtained for amorphous hafnium silicates using first-principles methods. Models of amorphous (HfO2)(x)(SiO2)(1-x) for varying x are generated by ab initio molecular dynamics. The calculations show that the presence of Hf gives rise to low-lying conduction states which explain the experimentally observed nonlinear dependence of the band gap on hafnium content. Static dielectric constants are found to depend linearly on x, supporting recent experimental data. (c) 2007 American Institute of Physics.