01428nas a2200205   4500008004100000245008900041210006900130260000800199300001000207490000700217520073100224100002600955700002600981700002101007700002301028700002101051700001701072700001901089856011401108       2008                        eng d00aIntroduction to the density matrix renormalization group ansatz in quantum chemistry0 aIntroduction to the density matrix renormalization group ansatz   cJAN  a49-650 v183 aThe Density Matrix Renormalisation Group (DMRG) is an electronic structure method that has recently been applied to ab-initio quantum chemistry. Even at this early stage, it has enabled the solution of many problems that would previously have been intractable with any other method, in particular, multireference problems with very large active spaces. Historically, the DMRG was not originally formulated from a wavefunction perspective, but rather in a Renormalisation Group (RG) language. However, it is now realised that a wavefunction view of the DMRG provides a more convenient, and in some cases more powerful, paradigm. Here we provide an expository introduction to the DMRG ansatz in the context of quantum chemistry.1 aChan, Garnet, Kin-Lic1 aDorando, Jonathan, J.1 aGhosh, Debashree1 aHachmann, Johannes1 aNeuscamman, Eric1 aWang, Haitao1 aYanai, Takeshi  uhttps://library.ncl.res.in/content/introduction-density-matrix-renormalization-group-ansatz-quantum-chemistry00603nas a2200145   4500008004100000245011600041210006900157260000800226490000800234100002100242700002300263700001900286700002600305856012600331       2008                        eng d00aOrbital optimization in the density matrix renormalization group, with applications to polyenes and ss-carotene0 aOrbital optimization in the density matrix renormalization group  cAPR0 v1281 aGhosh, Debashree1 aHachmann, Johannes1 aYanai, Takeshi1 aChan, Garnet, Kin-Lic  uhttps://library.ncl.res.in/content/orbital-optimization-density-matrix-renormalization-group-applications-polyenes-and-ss01939nas 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