A CONJUGATE-GRADIENT ALGORITHM WITH A TRUST REGION FOR MOLECULAR-GEOMETRY OPTIMIZATION

An algorithm is presented for the optimization of molecular geometries and general nonquadratic functions using the nonlinear conjugate grad ient method with a restricted step and a restart procedure. The algori thm only requires the evaluation of the energy function and its gradie nt and less memory storage is needed than for other conjugate gradient algorithms. Some numerical results are also presented and the efficie ncy and behaviour of the algorithm is compared with the standard conju gate gradient method. On the other hand we present comparisons of both conjugate gradient and variable metric methods with and without the t rust region technique. One of the main conclusions of the present work is that a trust region always improves the convergence of an optimitz ation method. A sketch of the algorithm is also given.