VB participants talks abstract page
Short talks will be given by volunteer participants. They should have a direct connection with VB theory. They may present, for instance, a recent research work connected with VB theory, a chemical problem on which a VB method or model could be relevant, or a method/algorithmic idea or scheme which could be of interest to the VB community. Presentation of open questions that could lead to discussions is welcome. Talks should be as compact and "straight to the point" as possible, and they should leave ample space for ideas exchange and discussions among the participants.
SPEAKERS : please add below, in your own section, your title talk and abstract :
- first : log in (see also : How to create an account) ;
- click on your name in the "Contents" box below, this will lead you to your own section ;
- your section starts with your name as the title line, click on [edit] (far right) ;
- To insert a file in your abstract, you will have to :
- upload your file (see : How to upload files on the wiki) ;
- then to insert the file in your text (see : How to insert files onto the wiki).
Duration of the talks will be 30 minutes including questions, so we recommend a <20 minutes talk in order to give space for discussions.
The order of abstracts follow the alphabetic order.
Celestino Angeli
Address, email
Title of the talk
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[[[Program_of_the_VB_workshop|<<< VB workshop program page]]
Jiali Gao
Address, email
Title of the talk
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[1]
[2]
Lynn Kamerlin
Address, email
Title of the talk
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[1]
[2]
Padeleimon Karafiloglou
Address, [1]
POLY-ELECTRON POPULATION ANALYSIS OF MO WAVEFUNCTIONS: A ‘theoretical microscope’ to explore local VB-type structures. (A proposition to extend this analysis for VB wavefunctions in order to explore molecular fragments such as ‘Functional Groups’)
Abstract...
References
[1] P. Karafiloglou, J. Chem. Phys. 130 (2009) 164103
[2] P. Papanikolaou, P. Karafiloglou, J. Phys. Chem. A 112 (2008) 8839
[3] P. Karafiloglou, J. Phys. Chem. A 105 (2001)4524
[4] P. Papanikolaou, P. Karafiloglou Chem. Phys. 342(2007)288
Christine Lepetit
Address, email
Title of the talk
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[1]
[2]
Jules Tshishimbi Muya
Address, email
Title of the talk
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[2]
Josep M. Oliva
Molecular Architectures built from Heteroborane Clusters: Electronic Structure and Beyond
In the last decade we have been interested in the electronic structure of heteroborane clusters [1], both in their groundstates and excited states. One of the challenges here is to build molecular architectures from heteroborane clusters in different dimensions and predict their shapes (geometries) and the electronic structures of their groundstates and low-lying states [2]. For instance, one can connect an S=1/2 heteroborane cage - CB(11)H(12)(·) - into an (in)finite 1D linear chain and map the electronic structure results onto a Heisenberg spin Hamiltonian [3]. Finally a VB interpretation of the many-electron problem within this field of research would be desirable [4].
References
[1] J.M. Oliva, N.L. Allan, P.v.R. Schleyer, C. Viñas, F. Teixidor, J. Am. Chem. Soc. 127 (2005) 13538-13547
[2] J.M. Oliva, D.J. Klein, P.v.R. Schleyer, L. Serrano-Andrés, Pure Appl. Chem. 81 (2009) 719-729
[3] J.M. Oliva, Adv. Quantum Chem., in press
[4] D.J. Klein, J.M. Oliva, Int. J. Quantum Chem. 110 (2010) 2784-2800
Carol Parish
Department of Chemistry, University of Richmond, email
Characterizing Heteroaromatic Diradicals
We are interested in the pyrolysis and combustion reactions of the molecular constituents of oil shale. Oil shale contains asphaltenes, a complex polydisperse molecular mixture, containing fused aromatic cores with long chain alkyl arms. In the high temperature regime, hydrogen abstraction reactions are possible forming heteroaromatic diradicals. We are in the process of characterizing properly diradical asphaltene model compounds – the diradicals of benzene, thiophene, fulvene, pyrrole and furan. A molecular orbital based approach will be presented along with preliminary results. Going forward, we would like to apply ab initio Valence Bond methods to the characterization of these molecules.
References
[1] An Extended Multireference Study of the Electronic States of para-benzyne, Evan Wang, Carol Parish and Hans Lischka, Journal of Chemical Physics, 2008 129, 44306:1-44306:8
Mario Piris
Address, email
The Molecular Orbitals in Natural Orbital Functional Theory
One-electron pictures have long helped to our understanding of chemical bonding. It has recently been pointed out that natural orbital functional theory (NOFT) can provide an orbital picture in agreement with the chemical intuition [1,2]. The NOFT appeared few decades ago [3,4]. An approximate NOF requires a reconstruction of the two-particle reduced density matrix (2-RDM) in terms of the one-particle reduced density matrix (1-RDM). Such reconstruction of the 2-RDM has been achieved using the cumulant expansion leading to the Piris NOF (PNOF) [5]. The PNOF is based on an explicit ansatz of the two-particle cumulant λ(Δ,Π) satisfying necessary N-representability conditions for the 2-RDM. Appropriate forms of matrices ∆ and Π lead to different implementations PNOFi (i=1,5) [6]. In this presentation, the theory behind the PNOF5 is briefly outlined. Some examples of strongly correlated systems, where density functionals yield pathological failures, are presented to illustrate the potentiality of the NOFT.
In this talk, we show that PNOF5 leads to two complementary representations of the one-electron picture in molecules, namely, the natural orbital (NO) representation and the canonical orbital (CO) representation. The PNOF5 NO representation leads generally to the localization of the molecular orbitals. Accordingly, it provides an orbital picture that agrees closely with the empirical valence shell electron pair repulsion theory (VSEPR) and the Bent's rule, along with the theoretical valence bond (VB) method. On the other hand, the equivalent CO representation, obtained from the diagonalization of the matrix of Lagrange multipliers, affords delocalized molecular orbitals adapted to the symmetry of the molecule. We show that the one-particle energies associated to the COs can yield reasonable principal ionization potentials. The relationship between NOs and COs is illustrated by several examples, showing that both orbital representations complement each other.
The calculations were carried out with our implementation, the PNOFID code [7], based on a recent proposed algorithm [8].
References
[1] J. M. Matxain, M. Piris, J. Uranga, X. Lopez, G. Merino, J. M. Ugalde, "The Nature of the Chemical Bonds from PNOF5 calculations", ChemPhysChem. DOI: 10.1002/cphc.201200205 (2012).
[2] J. M. Matxain, M. Piris, J. M. Mercero, X. Lopez, J. M. Ugalde, "sp3 hybrid orbitals and ionization energies of methane from PNOF5", Chem. Phys. Lett. 531, 272 (2012).
[3] T. L. Gilbert, Phys. Rev. B 12, 2111 (1975); M. Levy, Proc. Natl. Acad. Sci. U.S.A. 76, 6062 (1979); S. M. Valone, J. Chem. Phys. 73, 1344 (1980).
[4] M. Piris, "Natural Orbital Functional Theory" in Reduced-Density-Matrix Mechanics: With Applications to Manyelectron Atoms and Molecules, edited by D. A. Mazziotti, Adv. Chem. Phys. 134, 387 (2007), and references therein.
[5] M. Piris, "A new approach for the Two-Electron Cumulant in Natural Orbital Functional theory", Int. J. Quantum Chem. 106, 1093 (2006).
[6] M. Piris, "A natural orbital functional based on an explicit approach of the two-electron cumulant", Int. J. Quantum Chem. DOI: 10.1002/qua.24020 (2012).
[7] M. Piris, PNOFID, downloadable at http://www.ehu.es/mario.piris/#Software.
[8] M. Piris, J. M. Ugalde, "Iterative diagonalization for orbital optimization in the Natural Orbital Functional Theory", J. Comp, Chem. 30, 2078 (2009).
Romain Ramozzi
Address, email
Title of the talk
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[1]
[2]
Gustavo Scuseria
Department of Chemistry, Department of Physics and Astronomy, Rice University, Houston, Texas, USA, [2]
Projected HF and beyond: Is there a VB connection?
I will present our recent results on symmetry-projected wave functions [1,2]. For the Hartree-Fock case and spin projection, this is a 50-year old problem in quantum chemistry going back to Löwdin and his “extended HF” theory. For Hartree-Fock-Bogoliubov and number projection, our approach offers new perspectives on Antisymmetrized Geminal Power (AGP) wavefunctions that were the focus of much attention in the 1980s. In our work, all molecular symmetries (electron number, spin S^2 and S_z , point group, and complex conjugation) are deliberately broken and restored in a self-consistent variation-after-projection approach. The resulting method yields a comprehensive black-box treatment of static correlation with one-electron (mean-field) computational cost. The ensuing wave function is of high quality multireference character competitive with CASSCF. The method can also be applied to calculate excited states and spectral functions [3]. I will discuss applications to the Hubbard model and frustrated Heisenberg model (spin liquid). The curse of the thermodynamic limit (the method is not size consistent) and the quest for a low-cost treatment of residual correlations will also be addressed. More importantly, I am eager to discuss and learn about the connections of our projection methods with VB genealogy, particularly when we include several non-orthogonal determinants in our ansatz as we do in Ref. [3].
References
[1] Projected quasiparticle theory for molecular electronic structure, G. E. Scuseria, C. A. Jimenez-Hoyos, T. M. Henderson, J. K. Ellis, and K. Samanta, J. Chem. Phys. 135, 124108 (2011).
[2] Projected Hartree-Fock theory, C. A. Jimenez-Hoyos, T. M. Henderson, and G. E. Scuseria, J. Chem. Phys. 136, 164109 (2012).
[3] Symmetry-projected variational approach for ground and excited states of the two-dimensional Hubbard model, R. Rodrıguez-Guzman, K. W. Schmid, C. A. Jimenez-Hoyos, and G. E. Scuseria, Phys. Rev. B (2012) arXiv:1204.2006
Avital Shurki
Address, email
Valence Bond Insights on Enzyme Catalysis
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Matthias Stein
Address, email
Title of the talk
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Tom Ziegler
Analyzing Complex Electronic Structure Calculations on Large Molecules in Simple Chemical Terms
Abstract...In this talk we shall introduce a new scheme for chemical bond analysis [J. Chem. Theory Comput., 2009] by combining the Extended Transition State (ETS) method [Theor.Chim.Acta 1977,46,1] with the Natural Orbitals for Chemical Valence (NOCV) theory [J.Phys.Chem.A. 2008,112,1933]. The ETS-NOCV charge and energy decomposition scheme makes it not only possible to decompose the deformation density, Δρ, into the different components (such as σ,π,δ etc.) of the chemical bond, but it also provides the corresponding energy contributions to the total bond energy from these components. Thus, the ETS-NOCV scheme offers a compact, qualitative and quantitative, picture of the chemical bond formation within one common theoretical framework. Although, the ETS-NOCV approach contains a certain arbitrariness in the definition of the molecular subsystems that constitute the whole molecule, it can be widely used for the description of different types of chemical bonds. The applicability of the ETS-NOCV scheme is demonstrated for single (H3X-XH3, for X = C, Si, Ge, Sn) and multiple (H2X=XH2, H3CXXCH3, for X = C, Ge) covalent bonds between main group elements, for sextuple and quadruple bonds between metal centers (Cr2, Mo2, W2, [Cl4CrCrCl4]4-) and for double bonds between a metal and a main group element ((CO)5Cr=XH2, for X = C, Si, Ge, Sn). Applications are also given to hydrogen- and agostic bonds as well as the interaction between adsorbates and metal surfaces. The scheme is finally used to explain the trans-effect in square planar platimum complexes.
References
[1] Mariusz P. Mitoraj, Artur Michalak and Tom Ziegler “A Combined Charge and Energy Decomposition Scheme for Bond Analysis” J. Chem. Theory Comput., 2009,5 , 962–975