EFFECT OF EXCHANGE-CORRELATION FUNCTIONALS AND SYMMETRY CONSTRAINTS OF ELECTRONIC-STRUCTURE ON THE TRAJECTORIES OF REACTIVE MOLECULAR-COLLISIONS

Two computationally efficient implementations of first-principles mole cular dynamics are examined using the reactive scattering of two linea r ozone molecules to yield three molecules of oxygen. These methods ar e based on Kohn-Sham density-functional theory in which the charge den sity is fitted variationally. The linear combination of Gaussian-type orbitals approach is used to construct the orbital and local-potential basis sets. The first method is a completely general approach requiri ng variational fitting of the exchange-correlation energy density on a grid of points. The second method avoids the grid of joints, but is r estricted to the X alpha functional. Key elements of the dynamics calc ulation include self-consistent-field convergence at each time step, u se of fractional occupation numbers to model the configurational mixin g that occurs upon bond formation or dissociation, and accurate analyt ic evaluation of the appropriate forces acting upon the nuclei. Trajec tories computed using modern local-density and gradient-corrected func tionals, as well as X alpha (alpha = 0.6667) treated analytically, are compared. It is found that reactive trajectories obtained using analy tic X alpha and the generalized gradient approximation are very simila r when the initial kinetic energy is well above threshold for reaction . Under similar conditions, trajectories resulting from use of modern local-density functionals exhibit somewhat distinctive behavior. These results suggest that the particularly efficient analytic X alpha appr oach is suitable for preliminary investigations of chemical reactions using first-principles molecular dynamics based on density-functional theory. [S1050-2947(98)02502-5].