Ab initio molecular dynamics with an orbital-free density functional

A scheme for ab initio simulations of extended systems, which involves the use of the electron density as the basic variable, is discussed. The form of the kinetic energy functional is chosen to incorporate several exact limits (uniform system, linear response and rapidly varying density) while the rest of the energy functional is exactly the same as in a Kohn-Sham density functional calculation with the local density approximation. The authors' show that for sodium the present scheme yields high-quality results in a fraction of the time required with an orbital-based functional. The electronic part of the algorithm scales linearly with system size. An analysis of the stability of the method is made, and leads to criteria for selecting the non-physical parameters in the calculation so as to maximize the computational efficiency.