We have implemented and tested a frozen density matrix (FDM) approximation to the basic divide and conquer (DC) semiempirical algorithm. Molecular dynamics and Monte Carlo simulations were performed to estimate the advantages of the method. Results were compared to those obtained from the original DC method and the combined quantum mechanical/molecular mechanical (QM/MM) method, We found that the FDM approximation speeds DC calculations up significantly, while only introducing small errors. We also found that the FDM DC scheme performs better that the standard QM/MM approach in terms of defining the electronic and structural properties of the systems studied herein.