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 :
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- 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
Dipartimento di Chimica, Via Borsari 46, 44121 Ferrara (ITALY), email
VB reading of CASSCF wavefunctions: a few examples for ground and excited states.
A few recent studies in which the VB reading of CASSCF wavefunctions has been used to describe the electronic nature of ground and excited states of small and medium size molecules will be presented. Moreover, it will be shown how this analysis has allowed to unravel the origin of the peculiar difficulties found in the description of some systems, such as, for instance, the ionic excited states of conjugated molecules. In some cases, such a comprehension has enabled us to devise efficient MO-based computational approaches.
References
1] J.P. Malrieu, N. Guihery, C.J. Calzado, C. Angeli, Bond electron pair: its relevance and analysis from the quantum chemistry point of view, J. Comp. Chem., 28(1), 35-50, (2007).
[2] C. Angeli, R. Cimiraglia, J.P. Malrieu, On the relative merits of non-orthogonal and orthogonal Valence Bond methods illustrated on the hydrogen molecule, J. Chem. Ed., 85(1), 150-158, (2008).
[3] C. Angeli, J.P. Malrieu, Aromaticity: an ab-initio evaluation of the properly cyclic delocalization energy and of the <math>\pi</math>-delocalization energy distortivity in benzene, J. Phys. Chem. A, 112(45), 11481-11486, (2008).
[4] C. Angeli, On the nature of the <math>\pi\rightarrow\pi^*</math> ionic excited states: the V state of ethene as a prototype, J. Comp. Chem., 30(8), 1319-1333, (2009).
[5] C. Angeli, An analysis of the dynamic <math>\sigma</math> polarization in the V state of ethene, Int. J. Quant. Chem ., 110(13), 2436-2447, (2010).
[6] C. Angeli, C. J. Calzado, C. de Graaf, R. Caballol, The electronic structure of Ullman's biradicals: an orthogonal valence bond interpretation, Phys. Chem. Chem. Phys., 13(32), 14617-14628, (2011).
Samuel De Visser
My address, [1]
Enzymatic oxygen atom transfer reactions: Trends explained with Valence Bond Theory
Text of the abstract.
References
[1] ...
Jiali Gao
Multistate Density Functional Theory with Block-localized Configurations
In this paper, I will describe a multistate density functional theory (MSDFT) [1], in which the individual valence bond-like or diabatic states are represented through block-localization of Kohn-Sham orbitals[1,2]. The method is an extension of the mixed molecular orbital and valence bond (MOVB) method introduced by Yirong Mo and myself [3]. In MSDFT, dynamic correlation effects are incorporated into the localized diabatic configurations using BL-DFT. The multiconfiguration character of MSDFT, involving nonorthogonal determinant functions, consists of static correlation contributions. We try to discuss the issue of possible double counting correlation effects through model calculations [4]. Some specific applications will also be discussed including proton-coupled electron transfer and singlet fission.
References
[1] Cembran, J.; Song, L.; Mo, Y.; Gao, J. J. Chem. Theory Comput, 2009, 5, 2702.
[2] Mo, Y.; Song, L.; Lin, Y. J. Phys. Chem. A 2007, 111, 8291.
[3] Y. Mo, J. Gao, J. Phys. Chem. A, 2000, 104, 3012.
[4] Y. Mo, P. Bao, J. Gao,Phys. Chem. Chem. Phys., 2011, 13, 6760.
Lynn Kamerlin
Address, email
Chemistry-driven Protein Evolution in the Alkaline Phosphatase Superfamily
Shina Caroline Lynn Kamerlin1, Alexandre Barrozo1, Jinghui Luo1,2, Bert van Loo3
- Department of Cell and Molecular Biology (ICM), Uppsala University, Uppsala, Sweden
- Department of Biophysical and Structural Chemistry, Leiden Institute of Chemistry, Leiden University, Leiden, The Netherlands
- Department of Biochemistry, University of Cambridge, Cambridge, UK
The classical image of enzymes is that they are highly specific, with one enzyme catalysing one substrate. In recent years, it is becoming increasingly clear that many (if not even most) enzymes are capable of “promiscuous” catalytic activity, with one enzyme catalysing the turnover of multiple, chemically distinct, substrates. It has been suggested that such promiscuity can play an important role in the evolution of enzyme function1,2. The alkaline phosphatase superfamily provide a particular attractive showcase for testing this hypothesis, as the different members not only possess pronounced promiscuous activity, but also, they are “cross-promiscuous”, in that the native activity of one superfamily member is often a promiscuous activity in another3. Moreover, despite their deceptive similarity, the reactions catalysed by these enzymes (namely the cleavage of P-O and S-O bonds) proceed with very distinct solvation and protonation requirements4. We present here a detailed study of the promiscuous catalytic activity of two evolutionarily related (but structurally different) members of this superfamily, namely the arylsulfatase from Pseudomonas aeruginosa, as well as two related phosphonate monoester hydrolases. We demonstrate that, although subtle changes in the active site can have significant effects on the specificity, the promiscuity arises out of the ability of the non-native substrates to exploit the pre-existing electrostatic pre-organization of the active site towards the native substrate5,6. This, in turn provides an example of chemistry-driven protein evolution.
References
1) Khersonsky, O., Tawfik, D. S. (2010) Annu. Rev. Biochem. 79, 471-505.
2) Jensen, R. A. (1976) Annu. Rev. Microbiol. 30, 409-425.
3) Jonas, S. Hollfelder, F. (2009), Pure Appl. Chem. 81, 731-742.
4) Kamerlin, S. C. L. (2011) J. Org. Chem. 72, 9228-9238.
5) Luo, J., van Loo, B., Kamerlin, S. C. L. (2012) PROTEINS: Struct. Func. Bioinformat. 80, 1221-1226.
6) Luo, J. van Loo, B. Kamerlin, S. C. L. (2012) FEBS Lett.586, 1622-1630.
Padeleimon Karafiloglou
Address, [2]
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, as for example ‘Functional Groups’)
The first purpose of a general Poly-Electron Population Analysis (PEPA) is to calculate from usual MO wavefunctions the expectation values of general Eth order density operators, providing the probabilities of finding simultaneously E (in number) electrons in some target spin-orbitals. In a more general formulation, besides the E electrons one can consider H (in number) electron-holes; this gives the possibility to explore VB-type local structures from MO wavefunctions [1,2]. PEPA can be applied for both orthogonal and non-orthogonal orbitals, and our proposition in this workshop is to extend PEPA in order to analyze VB wavefunctions.
A variant of PEPA is the Natural PEPA (NPEPA), in which the analysis is performed in the basis of the physically meaningful Natural orbitals, developed in the framework of the NBO theory. NPEPA benefits of some basic features of these orbitals, and can calculate the probabilities P(E;H) (or, in general, the weights) of VB-type resonance structures of a target fragment of a molecule, as for example, of a ‘functional group’. NPEPA is different from NRT and VB methods; both provide information (i.e. weights of resonance structures)concerning the whole electronic assembly, while by means of NPEPA one can ‘place under the microscope’ any fragment of a given molecule and investigate the VB-type structures characterizing this fragment. For example, for pyrrole molecule one can ‘place under the microscope’ only the N atom, or, alternatively a C=C bond, or both in the N-C=C fragment (investigating the N lone pair delocalization) [1,2], etc, depending on the considered chemical problem.
Other possibilities of NPEPA (or PEPA) are: The explicit calculation of correlations (Coulomb and Exchange (or Fermi)), fluctuation of electrons in orbital spaces, and their (de)localization [3] - Establish useful relationships between the VB-type local structures [2] - Define the bond (de)localization within the VB language of resonance structures [4].- Provide a clear physical meaning for second quantized density operators and their relationships.
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
Laboratoire de Chimie de Coordination, 205 Route de Narbonne, 31077 Toulouse cedex 4. France, email
A three-level model for two-photon absorption. A combined Valence Bond and Electron Localization Function approach.
D. Kandaskalov, M. Vilhelmsen, C. Lepetit and R. Chauvin
This work is related to the design of carbo-meric chromophores with large two-photon absorption efficiency, a third order non-linear optical process with numerous (biomedical) applications (higher contrast imaging, photodynamic therapy, …) [1].
The high computational cost of the calculation of two-photon absorption cross-sections (σ2PA) makes exploratory studies difficult. A low-cost approximate calculation method would be desirable for a crude selection among the wide range of possible experimental targets, and thus for saving the performance of high level calculation [2] for promising chromophores only.
A two-form two-state VB model, early used to predict and analyze quadratic non-linear responses [3], can be transposed to a three-form three-state VB model to estimate σ2PA cross-sections from the weights of zwitterionic mesomeric forms resulting from the charge transfer related to the cubic non-linear optical response [4].
The method will be illustrated for quadrupolar carbo-benzenes [5] and the possibility for substituting the weights of the mesomeric forms obtained from VB theory by the ones obtained from topological analysis of the electron localization function (ELF) [6] will be discussed.
References
[1] M. Pawlicki, H. A. Collins, R. G. Denning, H. L. Anderson Angew. Chem. Int. Ed. 2009, 48, 3244.
[2] F. Terenziani, C. Katan, E. Badaeva, S. Tretiak, M. Blanchard-Desce Adv. Mater. 2008, 20, 4641.
[3] J. L. Oudar, J. Chemla J. Chem. Phys. 1977, 66, 2664.
[4] M. Barzoukas, M. Blanchard-Desce J. Chem. Phys. 2000, 113, 3951.
[5] L. Leroyer, C. Lepetit, A. Rives, V. Maraval, N. Saffon-Merceron, D. Kandaskalov, D. Kieffer, R. Chauvin Chem. Eur. J. 2012, 18, 3226.
[6] C. Lepetit, B. Silvi, R. Chauvin J. Phys. Chem. A 2003, 107, 464.
Jules Tshishimbi Muya
Chemical Bonding Analysis in boron and carbon buckyballs, B80 and C60
Jules Tshishimbi Muya1, Gopa Gopakumar2, Minh Tho Nguyen1 and Arnout Ceulemans1
1 Department of Chemistry, Katholieke Universiteit Leuven, B-3001 Leuven, Belgium 2 Max-Planck Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1 45470 Mülheim an der Ruhr, Germany
The boron fullerene B80 has received a lot of attention since the prediction of its theoretical stability by Szwacki et al. in 2007. This molecule is a spherical network of 80 boron atoms, which has a shape similar to the celebrated C60. The 80 borons span two orbits: an orbit of 60 atoms localised on the vertices of a truncated icosahedron like C60 and an orbit of 20 extra boron atoms capping the hexagons of the frame.
Quantum chemical calculations have shown that the B80 is unusually stable and has interesting physical (Bean et.al, Phys. Chem. Chem. Phys. 13 (2011), p.20855) and chemical properties (Muya et al., J. Phys. Chem. A, 115 (2011), p.9069). Its geometry is slightly distorted from Ih to Th symmetry. ( Muya et al., Chem. Phys. Lett. (2012), Accepted) Using Density Functional Theory at B3LYP/SVP level, we have analyzed the chemical bonding in B80. A symmetry analysis revealed a perfect match between the occupied molecular orbitals in B80 and C60. The cap atoms transfer their sp2 electrons to the truncated icosahedral frame, and they contribute essentially to the formation of σ- bonds. The frontier molecular orbitals have π character and they are localised on the B60 truncated icosahedral frame. ( A.Ceulemans et al., Chem. Phys. Lett. 461 (2008), p. 226.)
References
[1] A Ceulemans, JT Muya, G Gopakumar, MT Nguyen, Chem. Phys. Lett. 461 (2008), p. 226.
[2] D Bean, JT Muya, P Fowler,MT Nguyen, A Ceulemans, Phys. Chem. Chem. Phys. 13 (2011), p.20855.
[3]JT Muya, F De Proft, P Geerlings, MT Nguyen, A Ceulemans, J. Phys. Chem. A 115 (2011), p.9069.
[4] JT Muya, E Lijnen,M Nguyen,A Ceulemans,J.Phys.Chem. A 115 (2011), p.2268.
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
A Valence Bond study of isocyanides' electronic structure
Since their first synthesis in 1859, isocyanides remained marginal for decades due to their difficult access and repulsive smell. Nevertheless, the reactivity of the terminal carbon and their use in the most famous multicomponent coupling, the Ugi reaction, initiated their revival during the past ten years. However, the representation still remains unclear as 2 forms are still used by organic chemists. Are they best described as a carben, a zwiterrion or a resonance mixing of both ? Does the picture change with the substituants and/or with the solvent ? High level Valence bond calculations are performed to answer these questions.
References R. Ramozzi, N. Chéron, B. Braïda, P. C. Hiberty, P. Fleurat-Lessard, New. J. Chem, 2012, 36, 1137-1140.
Zahid Rashid
Theoretical Chemistry Group, Utrecht University, The Netherlands, email
A Quadratically Convergent VBSCF Method
A quadratically convergent Valence Bond Self-Consistent Field (VBSCF) method[1-3] will be described where the simultaneous optimisation of orbitals and VB-structure coefficients is based on Newton-Raphson scheme. The efficiency of the method, in comparison with Super- CI, will be discussed using the results of some test calculations with VB-local and VB-delocal orbital-optimisation models.
References
1. van Lenthe, J. H.; Balint-Kurti, G. G. Chem. Phys. Lett. 1980, 76, 138--142.
2. van Lenthe, J. H.; Balint-Kurti, G. G. J. Chem. Phys. 1983, 78, 5699--5713.
3. van Lenthe, J. H.; Dijkstra, F.; Havenith, R. W. A. TURTLE - A gradient VBSCF Program Theory and Studies of Aromaticity. In Theoretical and Computational Chemistry: Valence Bond Theory; Cooper, D. L., Ed.; Elsevier: Amsterdam, 2002; Vol. 10, pp 79--116.
Avital Shurki
Address, email
Valence Bond Insights on Enzyme Catalysis
Tom Ziegler
Analyzing Complex Electronic Structure Calculations on Large Molecules in Simple Chemical Terms
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