01939nas a2200169   4500008004100000245012400041210006900165260000800234300001400242490000800256520129700264100001901561700002001580700002101600700002601621856012201647       2009                        eng d00aAccelerating convergence in iterative solution for large-scale complete active space self-consistent-field calculations0 aAccelerating convergence in iterative solution for largescale co  cAUG  a2178-21900 v1093 aAn algorithm that accelerates the convergence of the iterative optimization of the complete active space self-consistent field (CASSCF) wavefunction so as to find a optimum solution in fewer macroiterations is described. The algorithm is oriented to large-scale CASSCF problems that are to be solved with a combination of density matrix renormalization group (DMRG) method for the configuration interaction (CI) process. The algorithm is based on the alternating (or two-step) CASSCF optimization in which the CI and molecular orbital (MO) parameters are optimized separately. Convergence ratio is improved by finding further optimized MOs from a linear extrapolation of the MO sets of the iteration history. The acceleration results in fewer diagonalizations in a total CASSCF calculation to save a considerable computational cost. The convergence performance is examined in a couple of realistic applications on SiC(3) and poly (phenyl)carbenes. For poly(phenyl)carbenes, the large-size CASSCF calculations with CAS(30e,30o) that entails full pi valence space as well as sp(2) orbital space of carbenes are performed by using the practical implementation of DMRG-CASSCF in conjunction with the acceleration technique. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 109: 2178-2190, 20091 aYanai, Takeshi1 aKurashige, Yuki1 aGhosh, Debashree1 aChan, Garnet, Kin-Lic  uhttps://library.ncl.res.in/content/accelerating-convergence-iterative-solution-large-scale-complete-active-space-self