Single point UHF calculations

Performing Single-Point UHF Calculations on the Simplified Ni Complexes... 

Record the final energies (eV) obtained for each geometry in the triplet and singlet states obtained from your single-point UHF calculations. Check (V) the preferred spin state of each geometry. 

The toluene radical cation provides a good example of how difficult converging a calculation to the electronic ground state of an open-shell molecule can be. If one does a single-point UHF/3-21G calculation at the equilibrium geometry of the neutral molecule, in which one hydrogen atom of the methyl group lies... 

The unrestricted and restricted open-sheU Hartree-Fock Methods (UHF and ROHF) for crystals use a single-determinant wavefunction of type (4.40) introduced for molecules. The differences appearing are common with those examined for the RHF LCAO method use of Bloch functions for crystalline orbitals, the dependence of the Fock matrix elements on the lattice sums over the direct lattice and the Brillouin-zone summation in the density matrix calculation. The use of one-determinant approaches is the only possibility of the first-principles wavefunction-based calculations for crystals as the many-determinant wavefunction approach (used for molecules) is practically unrealizable for the periodic systems. The UHF LCAO method allowed calculation of the bulk properties of different transition-metal compounds (oxides, perovskites) the qrstems with open shells due to the transition-metal atom. We discuss the results of these calculations in Chap. 9. The point defects in crystals in many cases form the open-sheU systems and also are interesting objects for UHF LCAO calculations (see Chap. 10). 

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