A LINEAR LEAST-SQUARES VARIATIONAL RECIPE FOR THE CALCULATION OF APPROXIMATE ENERGY EIGENSTATES

The efficacy of the energy-spread minimization technique for solving t he energy-eigenvalue equation in a linear variational framework is ass essed with a 3 x 3 matrix perturbation problem with backdoor intruders , quartic anharmonic oscillator and the He-atom problems as prototypic al examples. Both direct and indirect minimization schemes are conside red and disadvantages of the latter pointed out. The relative merits a nd demerits of the conventional, vis-a-vis stochastic minimization rou tes are critically analyzed in the present context.