I'm reviewing the PDB data, being largely ignorant of molecular biology, I have a question regarding experimental models vs theoretical models. Why are there so few theoretical models in the PDB as opposed to experimental models based on x-ray crystallography and NMR, which make up the vast majority of structural models in the PDB?

Only 2% of the models are considered theoretical. In the advanced search there is no category to search for these theoretical models (except possibly 'other' when it comes to experimental method).

I understand they are less accurate. Is there a threshold of accuracy? How about another resource beside the PDB that provides access to these theoretical models for mining purposes or else for research on a particular molecule?