TITLE HF-HF OPT SYMMETRY CS END BASIS 631G** VARIABLES RFF 2.75 A RFH1 0.912 A RFH2 0.912 A THETA1 5.0 D THETA2 -110.0 D END ATOMS F1 9 0 0 0 F2 9 0 0 RFF H1 1 POL RFH1 THETA1 0 H2 1 PTC F2 F1 H1 RFH2 THETA2 END OPTIMISE START FINISHThis example sets up the initial geometry in internal coordinates, the the initial values of the parameters declared as variables. The OPTIMISE keyword causes a geometry optimisation to be carried out resulting in an optimised geometry after several steps.
The gradients on each step are displayed in the following form - the gradient is in internal coordinates because the geometry was specified in those coordinates.
Parameter value gradient name (bohr or (angstrom radian) or degree) RFF 5.15702682 2.72898127 0.00009552 RFH1 1.70967460 0.90472090 0.00000851 RFH2 1.70772980 0.90369176 -0.00000904 THETA1 0.24962520 14.30247061 0.00000922 THETA2 -1.77558739 -101.73366372 0.00002072This is actually the final set of parameters corresponding to the minimum. The final geometry is also given in cartesian coordinates. If the initial geometry had been given in cartesian coordinates then the gradient on each step would also be printed in cartesians, in the format described in the first section in this chapter.
At the end of the optimisation, various properties of the molecule are given - charge densities, atomic populations, dipole and quadrupole moments, the electric fields at the nuclei and the moments of inertia and rotational constants. These are generated automatically and correspond to a call of the PROPERTY directive (see section 6.1).
The above example is for closed-shell SCF, however other types of wavefunction are just as simple - all one has to do is include those directives which specify the type of energy calculation ie closed or open-shell SCF, and whether correlation is included. For example, an MP2 optimisation simply requires the addition of the keyword MP2 to the above dataset.