The use of computational chemistry to address issues relative to process design is discussed. The need for efficient software for massively parallel architectures is described. Methods to predict the electronic structure of molecules are described for the molecular orbital and density functional theory approaches. The capabilities of the computational chemistry software NWChem and Ecce developed in the Environmental Molecular Sciences Laboratory are discussed. Two examples of electronic structure calculations are given. The first shows that one can now make extremely accurate predictions of the thermochemistry of small molecules if one carefully considers all of the details such as zero point energies, core-valence corrections, and relativistic corrections. The second example shows how more approximate computational methods, still based on high level electronic structure calculations, can be used to address a complex waste processing problem at a Department of Energy nuclear production facility.