  The use of energy functionals based on density as the basic variable is
advocated for ab initio molecular dynamics. It is demonstrated that the
constraint of positivity of density can be incorporated easily by using square
root density for minimization of the energy functional. An ad hoc prescription
for including nonlocal pseudopotentials for plane wave based calculations is
proposed and is shown to yield improved results. Applications are reported for
equilibrium geometries of small finite systems, viz. dimers and trimers of
simple metal atoms like Na and Mg, which represent a rather stringent test for
approximate kinetic energy functionals involved in such calculations.
