Articles you may be interested inThe complex scaled multiconfigurational time-dependent Hartree-Fock method for studying resonant states: Application to the 2s 2 He Feshbach resonance J. Chem. Phys. 140, 094305 (2014); 10.1063/1.4867059The coupled cluster approach with a hybrid treatment of connected triple excitations based on the restricted Hartree-Fock reference J. Chem. Phys. 134, 044134 (2011); 10.1063/1.3541250
Hartree-Fock orbitals for complex-scaled configuration interaction calculation of highly excited Feshbach resonancesA localized molecular-orbital assembler approach for Hartree-Fock calculations of large molecules A method is proposed for the solution of the self-consistent field equations that can lead to localized occupied and virtual molecular orbitals, avoiding the need for solving for the canonical molecular orbitals. The method starts with strongly localized ''guess molecular orbitals'', it is nonperturbative and proceeds through the diagonalization of single configuration interaction matrices which may be rendered size-consistent through appropriate coupled electron pair approximation or coupled-cluster-type dressings. We see a potential utility for the method in applications to large systems where localized orbitals will improve the scaling of the computational resources required with increasing system size.
For the ternary thioferrate crystal Na 6 Fe 2 S 6 , ab initio quantum chemical calculations using a cluster model ansatz have been performed to examine the magnetic coupling of the two half-filled Fe 3d shells in the isolated dimeric [Fe 2 S 6 ] 6complexes having the structure of edge-linked double tetrahedra. The activeelectron approach using complete active space configuration interaction (CASCI) with 10 electrons in 10 orbitals yields the multiplet splitting of a two-center Heisenberg Hamiltonian with an antiferromagnetic coupling constant J ) -19 cm -1 , which is by a factor of 5 smaller than the experimental value. Correlation effects are essential for the magnetic coupling, as the application of multireference second-order Møller-Plesset perturbation theory based on the CIPSI algorithm (CAS-2nd) and the recently proposed difference-dedicated CI method lead to values J(4f5) ) -158 and -66 cm -1 , respectively, which clearly agree better with experiment. The different electronic contributions to the chemical bonding in the binuclear transition metal complex have been investigated using the constrained space orbital variation method.
Localized molecular Hartree᎐Fock orbitals have been determined by means of an iterative procedure consisting of orthogonalization and configuration interaction employing single excitations. For ring systems the rotational symmetry has been included explicitly to obtain Wannier-like orbitals suited for a posteriori correlation calculations using only the most important contributions within a limited region around one reference ring segment. Applications involving different estimates of the correlation Ž . energy include as model systems H , the ionic Li H , and a weakly bound 2 2nq1 n n Ž . beryllium ring as well as the strongly covalent molecule CH forming a closed ring.
36In all cases, the localized and canonical MP2 results are close, and the localized Epstein᎐Nesbet second-order gives a good estimate of more expensive MP4 or CEPA-0 values.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.