| Abstract: | Analytical second derivatives of the energy are derived and efficiently implemented for semiempirical MNDO-type methods including AM1, PM3, and MNDO/d. A new algorithm for the simultaneous solution of several CPHF equations is proposed in which the amount of memory required is independent of the number of iterations. The analytical approach is faster than the numerical approach typically by a factor of 5 and exhibits a reliable convergence over a wide range of molecules. The asymptotic memory and secondary storage requirements of the reported procedure can be as low as O(N2) without significant degradation of the performance. © 1996 by John Wiley & Sons, Inc. |
