[ { "id": "authors:ycn2x-18b11", "collection": "authors", "collection_id": "ycn2x-18b11", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180731-132413916", "type": "article", "title": "Multiconfiguration wavefuntions for the lowest (\u03c0\u03c0*) excited states of ethylene", "author": [ { "family_name": "Bender", "given_name": "Charles F.", "clpid": "Bender-Charles-F" }, { "family_name": "Dunning", "given_name": "Thom. H., Jr.", "clpid": "Dunning-T-H" }, { "family_name": "Schaefer", "given_name": "Henry F., III", "clpid": "Schaefer-H-F-III" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Hunt", "given_name": "William J.", "clpid": "Hunt-W-J" } ], "abstract": "Ab initio calculations have been carried out for the T(^(3)B_(1u)) and V(^(1)B_(1u)) states of ethylene in a planar nuclear configuration. A \"double-zeta\" gaussian basis, augmented by diffuse functions, was used. A wide variety of configuration interaction wavefunctions (including as many as 1605 configurations), optimized by the iterative natural orbital method, were computed. The calculations predict the ^(1)B_(1u) state to lie 3.8 \u2013 4.1 eV above the 3B1u state. The spatial extent of the triplet state is that of a normal valence state with (x2) \u2248 12 bohr^2. The singlet state, on the other hand, is found to be quite diffuse or Rydberg-like, (x^2) \u2248 35 bohr^2; electron correlation was found to decrease (x^2) by 30% from the Hartree - Fock value (52 bohr^2). This result is not consistent with simple notions concerning \u03c0-electron theory.", "doi": "10.1016/0009-2614(72)80143-X", "issn": "0009-2614", "publisher": "Elsevier", "publication": "Chemical Physics Letters", "publication_date": "1972-08-01", "series_number": "2", "volume": "15", "issue": "2", "pages": "171-178" }, { "id": "authors:1qzpy-3b826", "collection": "authors", "collection_id": "1qzpy-3b826", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180720-135500279", "type": "article", "title": "The incorporation of quadratic convergence into open-shell self-consistent field equations", "author": [ { "family_name": "Hunt", "given_name": "William J.", "clpid": "Hunt-W-J" }, { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Dunning", "given_name": "Thom. H., Jr.", "clpid": "Dunning-T-H" } ], "abstract": "The quadratically convergent approach to solving the correct SCF equations for general open-shell systems (with orthogonal orbitals, i.e., multiconfiguration-SCF or Hartree-Fock) is derived and used to discuss other less complicated approaches. Representative calculations on He ^21[(1s) (2s)] and H_2O 2^1A_1 [(1a_1)^2 (2a_1)^2 (1b_1)^2 (1b^2)_2 (3a_1) (4a_1)] are reported.", "doi": "10.1016/0009-2614(70)80202-0", "issn": "0009-2614", "publisher": "Elsevier", "publication": "Chemical Physics Letters", "publication_date": "1970-08-01", "series_number": "3", "volume": "6", "issue": "3", "pages": "147-151" }, { "id": "authors:g354m-30x18", "collection": "authors", "collection_id": "g354m-30x18", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180712-121222509", "type": "article", "title": "The proper treatment of off-diagonal Lagrange multipliers and coupling operators in self-consistent field equations", "author": [ { "family_name": "Goddard", "given_name": "William A., III", "orcid": "0000-0003-0097-5716", "clpid": "Goddard-W-A-III" }, { "family_name": "Dunning", "given_name": "Thom. H.", "clpid": "Dunning-T-H" }, { "family_name": "Hunt", "given_name": "William J.", "clpid": "Hunt-W-J" } ], "abstract": "We show that past treatments of the off-diagonal Lagrange multipliers or coupling operators in the self-consistent field equations for open-shell systems and in the multi-configuration SCF equations are incomplete. In addition, we obtain the complete variational equations and show how these may be combined into one simple eigenvalue problem which is solved for all orbitals.", "doi": "10.1016/0009-2614(69)80170-3", "issn": "0009-2614", "publisher": "Elsevier", "publication": "Chemical Physics Letters", "publication_date": "1969-11-15", "series_number": "5", "volume": "4", "issue": "5", "pages": "231-234" }, { "id": "authors:2cmrn-qga35", "collection": "authors", "collection_id": "2cmrn-qga35", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120815-113718356", "type": "article", "title": "Nonempirical Calculations on Excited States: The Ethylene Molecule", "author": [ { "family_name": "Dunning", "given_name": "Thom. H.", "clpid": "Dunning-T-H" }, { "family_name": "McKoy", "given_name": "Vincent", "clpid": "McKoy-V" } ], "abstract": "A series of nonempirical calculations are reported on the excited states of the ethylene molecule using a recent minimum basis set LCAO MO SCF wavefunction. For the lowest excited singlet state of ethylene (^1B_(3u)) the coupling between the \u03c0 electrons and \u03c3 electrons is significant: the excitation energy being decreased from 11.98 to 10.17 eV and the oscillator strength from 1.03 to 0.73. This coupling has little effect on the triplet state. In the next higher approximation (the random\u2010phase approximation) the excitation energy is further decreased to 9.44 eV and the transition moment to 0.51. With the use of accurate LCAO MO SCF wavefunctions, it is felt that the methods presented here will provide a basis for the theoretical interpretation of electronic spectra.", "doi": "10.1063/1.1712158", "issn": "0021-9606", "publisher": "American Institute of Physics", "publication": "Journal of Chemical Physics", "publication_date": "1967-09-01", "series_number": "5", "volume": "47", "issue": "5", "pages": "1735-1747" } ]