Abstract:
Methods for both partial and full optimization of wavefunction
parameters are explored, and these are applied to the LiH molecule. A
partial optimization can be easily performed with little difficulty. But to
perform a full optimization we must avoid a wrong minimum, and deal with
linear-dependency, time step-dependency and ensemble-dependency
problems. Five basis sets are examined. The optimized wavefunction with a
3-function set gives a variational energy of -7.998 + 0.005 a.u., which is
comparable to that (-7.990 + 0.003) 1 of Reynold's unoptimized \fin ( a
double-~ set of eight functions). The optimized wavefunction with a double~
plus 3dz2 set gives ari energy of -8.052 + 0.003 a.u., which is comparable
with the fixed-node energy (-8.059 + 0.004)1 of the \fin. The optimized
double-~ function itself gives an energy of -8.049 + 0.002 a.u. Each
number above was obtained on a Bourrghs 7900 mainframe computer with
14 -15 hrs CPU time.
