| 1. |
- Borin, Antonio Carlos, et al.
(författare)
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A theoretical study of the binding and electronic spectrum of the Mo-2 molecule
- 2008
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 343:2-3, s. 210-216
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Tidskriftsartikel (refereegranskat)abstract
- Multiconfigurational SCF and second-order perturbation theory have been employed to study seven low-lying singlet and triplet electronic states of the Mo-2 molecule. The bond order of the ground state has been analyzed based on the effective bond order (EBO), indicating that a fully developed sextuple bond is formed between the two Mo atoms. The experimentally observed excited states a(3)Sigma(+)(u) and A(1)Sigma(+)(u) have been determined and the so-called (3)Lambda excited state identified as the b(3)Sigma(+)(u) state, in agreement with experimental expectations.
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| 2. |
- Borin, Antonio Carlos, et al.
(författare)
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Electronic structure and chemical bonding in the ground states of Tc-2 and Re-2
- 2009
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Ingår i: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 107:8-12, s. 1035-1040
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Tidskriftsartikel (refereegranskat)abstract
- Multiconfiguration second-order perturbation theory, including relativistic effects and spin-orbit coupling, has been employed to investigate the nature of the chemical bonding in the ground state of Tc-2 and Re-2. The Tc-2 ground state is found to be a 0(g)(+) state, with an effective bond order (EBO) of 4.4, and a dissociation energy of 3.25 eV. The Re-2 ground state is a 1(g) state, with EBO = 4.3. Almost degenerate to it, is a 0(g)(+) state (T-e = 77 cm(-1)), with EBO = 4.1. Experimental evidence also indicates that the ground state is of 1(g) nature. The dissociation energy is computed to be 5.0 eV in agreement with an experimental estimate of 4 +/- 1 eV.
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| 3. |
- Borin, Antonio Carlos, et al.
(författare)
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Electronic structure and chemical bonding in W-2 molecule
- 2010
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 490:1-3, s. 24-28
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the lowest-lying electronic states of W-2 were investigated at the CASPT2 level. The ground state is a X-1 Sigma(+)(g) state, followed by the a(3)Delta(u), b(3)Sigma(+)(u) and A(1)Delta(u) electronic states. Seven low-lying Omega-states were computed: (1)0(g)(+), (2)3(u), (3)2(u), (4)1(u), (5)0(u)(-), (6)1(u), and (7)2(u), with the ground state corresponding to the (1)0(g)(+)(X-1 Sigma(+)(g)) state. Comparison with the other VIB transition metal group dimers indicates a common pattern of electronic structure and spectroscopic properties. (C) 2010 Elsevier B.V. All rights reserved.
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| 4. |
- Gobbo, Joao Paulo, et al.
(författare)
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On the Deactivation Mechanisms of Adenine-Thymine Base Pair
- 2012
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 116:13, s. 4089-4097
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution, the multiconfigurational second-order perturbation theory method based on a complete active space reference wave function (CASSCF/CASPT2) is applied to study all possible single and double proton/hydrogen transfers between the nucleobases in the adenine-thymine (AT) base pair, analyzing the role of excited states with different nature [localized (LE) and charge transfer (CT)] and considering concerted as well as step-wise mechanisms. According to the findings, once the lowest excited states, localized in adenine, are populated during UV irradiation of the Watson-Crick base pair, the proton transfer in the N-O bridge does not require high energy in order to populate a CT state. The latter state will immediately relax toward a crossing with the ground state, which will funnel the system to either the canonical structure or the imino-enol tautomer. The base pair is also capable of repairing itself easily since the imino-enol species is unstable to thermal conversion.
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| 5. |
- Roos, Björn, et al.
(författare)
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New Relativistic Atomic Natural Orbital Basis Sets for Lanthanide Atoms with Applications to the Ce Diatom and LuF3
- 2008
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 112:45, s. 11431-11435
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Tidskriftsartikel (refereegranskat)abstract
- New basis sets of the atomic natural orbital (ANO) type have been developed for the lanthanide atoms La-Lu. The ANOs have been obtained from the average density matrix of the ground and lowest excited states of the atom, the positive ions, and the atom in an electric field. Scalar relativistic effects are included through the use of a Douglas-Kroll-Hess Hamiltonian. Multiconfigurational wave functions have been used with dynamic correlation included using second-order perturbation theory (CASSCF/CASPT2). The basis sets are applied in calculations of ionization energies and some excitation energies. Computed ionization energies have an accuracy better than 0.1 eV in most cases. Two molecular applications are inluded as illustration: the cerium diatom and the LuF3 molecule. In both cases it is shown that 4f orbitals are not involved in the chemical bond in contrast to an earlier claim for the latter molecule.
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| 6. |
- Ryde, Ulf, et al.
(författare)
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A theoretical study of the copper–cysteine bond in blue copper proteins
- 2001
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Ingår i: Theoretical Chemistry Accounts. - : Springer Science and Business Media LLC. - 1432-881X. ; 105:6, s. 452-462
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Tidskriftsartikel (refereegranskat)abstract
- The accuracy of theoretical calculations on models of the blue copper proteins is investigated using density functional theory (DFT) Becke's three-parameter hybrid method with the Lee–Yang–Parr correlation functional (B3LYP) and medium-sized basis sets. Increasing the basis set to triple-zeta quality with f-type functions on all heavy atoms and enlarging the model [up to Cu(imidazole-CH3)2(SC2H5) (CH3SC2H5)0/+] has only a limited influence on geometries and relative energies. Comparative calculations with more accurate wave-function–based methods (second-order Møller–Plesset perturbation theory, complete-active-space second-order perturbation theory, coupled-cluster method, including single and double replacement amplitudes and in addition triple replacement perturbatively) and a variety of basis sets on smaller models indicate that the DFT/B3LYP approach gives reliable results with only a small basis set dependence, whereas the former methods strongly depend on the size of the basis sets. The effect of performing the geometry optimizations in a continuum solvent is quite small, except for the flexible Cu-SMet bond. The results of this study confirm the earlier results that neither the oxidized nor the reduced copper site in the blue proteins is strained to any significant degree (in energy terms) by the protein surrounding.
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