Geometry optimization with an infinite basis set

We show that geometries can be optimized directly at a level corresponding to extrapolation to an infinite basis set. Numerical examples demonstrate t hat geometries obtained with gradients extrapolated to the infinite-basis l imit agree well with geometries calculated with much bigger basis sets than those used for the calculation. The method may also be used to calculate r eaction paths or classical trajectories directly at the extrapolated infini te-basis limit.