Direct determination of the density matrix using the density equation: potential energy curves of HF, CH4, BH3, NH3, and H2O

The density equation (DE) method was utilized for calculations of the potential energy curves of the molecules HF, CH4, BH3, NH3, and H2O. The equilibrium geometries and the vibrational force constants of these molecules were determined by the DE method without any use of the wavefunction. The calculated values are in close agreement with the results of the symmetry-adapted cluster (SAC) and full-CI methods.