INTRODUCTION

RESEARCH OVERVIEW

The central research topic of the General Chemistry Research group (ALGC: “Onderzoeksgroep Algemene Chemie”) is quantum chemistry., i.e. the application of quantum mechanics to chemical problems such as the structure, stability and reactivity of molecules. The group more specifically focuses on the fundamental and applied aspects of Density Functional Theory (DFT). Based on the famous Hohenberg and Kohn theorems, this theory uses the electron density of the system as the basic carrier of information of an atomic or molecular system instead of the wave function. It can be undoubtedly stated that DFT has revolutionized quantum chemistry in the past three decades; within the Kohn-Sham framework, DFT has been turned into a computational workhorse, which is now used not only by quantum chemists, due to its capability to treat systems of ever increasing size at moderate computational cost, but also by experimental chemists active in various different branches of chemistry. 


This computational breakthrough has been accompanied by a second revolution, launched by Parr and coworkers in the late seventies and early eighties. Within the DFT context, a large number of very popular but previously often vaguely defined chemical concepts, such as e.g. electronegativity, hardness and softness, useful in describing and interpreting atomic and molecular electronic structure, and their variation upon chemical reactions, were sharply defined, thus affording their numerical evaluation.


This branch was termed Conceptual DFT by its founding father and has been the central theme of research of the ALGC group for more than 25 years, leading to international recognition. “Conceptual DFT” is based on the fact that when a molecule is involved in a chemical reaction, it ultimately undergoes a change in its number of electrons N and/or its external potential v(r) (for an isolated system, this external potential is just the potential due to the nuclei of the system). The energy change upon these changes can be quantified by a Taylor series expansion in which the energy derivatives are associated to chemical concepts, thus naturally providing a connection between energy changes and concepts.  The reactivity of a given species (atom, molecule, functional group, …) can thus be described on the basis of its isolated system properties in a perturbational approach using model perturbations, i.e. through a "perturbational perspective on chemical reactivity".


This main research topic of the ALGC group resulted in the development and use of DFT-based concepts for describing the behavior of molecules, in particular in their reactions. Fundamental and applied work, often in direct collaboration with experimentalists have been combined.


Fundamental work has been done on the development of density functional theory based descriptors of molecular charge distribution and reactivity (eg. local hardness, shapefunction, (nuclear) Fukui functions, spin polarized extensions, linear response function) and on the development and/or testing related or testing related principles (the Hard and Soft Acids and Basis Concept, the Maximum Hardness Principle). In recent years, the linear response function of atoms and molecules (computation, representation and interpretation with link to traditional concepts such as inductive and resonance effects, (anti)-aromaticity, local polarizability was particularly focused on applications have been considered in organic and inorganic chemistry, in catalysis, biochemistry, and nanomaterials chemistry.


Both kinetic and thermodynamic aspects were considered of reactions in gas phase, solution and at surfaces. Substrates and topics studied, often in direct interaction with experimental groups, are catalytic and adsorption properties of zeolites, adsorption on silver surfaces, electronic and mechanical properties of fullerenes, physical and chemical properties of nanotubes, and graphene (including adsorption of polymers), stability and reactivity of radicals, (unusual) bonding situations in main group elements… Different types of organic reactions have been studied, from the classical addition, substitution and elimination reactions to pericyclic reactions. In recent years complexation and redox reactions in inorganic and biochemistry (redoxbiology) have been a particular focus, including also problems of homogeneous catalysis.


In a natural way, several new research lines developed on the basis of the aforementioned experience and interests and are together with the continuing developments in conceptual DFT, the present research highlights of the group.


The linear response function was a perfect guide to launch a research line in molecular electronics: controlling the conductivity properties of molecular devices is a fascinating field where physical, organic and theoretical chemistry meet.


The experience built up in the study of aromaticity and its change upon acid base, or redox reaction was a starting point to investigate the molecular switching properties of extended porphyrins which change their conformation as a function of external stimuli (pH, solvent, metalation) thereby sometimes adopting Mobius ring conformations. Noncovalent interactions, such as Hydrogen bonding and dispersion are prominent in these processes.


On the basis of our experience with the evaluation and interpretation of molecular stability and reactivity a completely new line was launched in the field of inverse design, i.e. creating -in silico - molecules with well-defined and optimized properties. These large-scale calculations will ultimately guide experimental synthetic chemists in their time and money consuming exploration of Chemical Space.


Turning conceptual DFT into a predictive mode (i.e. to predict and no longer interpret) becomes a fundamental ingredient of the research activities. In order to obtain this level reactivity and reactions are to be studied in the molecule’ s real environment which in most cases involves a solvent. The free energy surface for chemical transformations in solution may have a very complex nature. The ALGC group recently gained considerable experience in ab initio molecular dynamics and metadynamics simulations to unravel organic chemistry reaction mechanisms. This will go hand in hand with the design of protocols to accurately compute solution phase reactivity indices.  


The research in all above mentioned directions, both fundamental and applied, is continued with a group with size around 20 members (graduate and doctoral students and postdoctoral fellows). Extensive collaboration or frequent contacts have been established with research groups inside the VUB in the Faculty of Sciences and Applied Sciences, in other Belgian Universities (Antwerp, Leuven, Ghent, ...), with the Janssen Pharmaceutica Foundation, Exxon Mobil, Mallinckrodt, Solvay and with numerous Universities abroad (Cracow, Wroclaw, Erlangen, Exeter, Pune, North Carolina, Mc Master, Girona, Hyderabad, Budapest, Santiago, Durham, Duke, Pardubice, Ljubljana, Amsterdam, Basel, Cornell, Paris VI,...)

Since 20 years the group has been the nucleus of a Scientific Research Network (Wetenschappelijke Onderzoeksgemeenschap) of the Fund for Scientific Research (Flanders) on Density Functional Theory, a consortium of 9 Belgian and 9 Foreign groups. This consortium has been the basis of the organization of the "10th International Conference on the Applications of Density Functional Theory in Chemistry and Physics" held at the VUB from 7 - 12 september 2003 and which has been presided by P. Geerlings. On April 5-7, 2005 a three Day International Symposium on Theoretical Aspects of Chemical Reactivity was organized by this network in collaboration with the International Solvay Institutes for Physics and Chemistry. From April 1-6-2012 the VUB group and their Ghent Alliance Partner organize "Challenges in Density Matrix Theory", an international conference with 23 renowned speakers in Ghent. On october 22 -2014, a one day Symposium on Molecular Electrostatic Potentials in honor of Prof. Gadré was organized.
In April 2016, a Solvay workshop entitled “Conceptual Quantum Chemistry: Present Aspects and Challenges for the Future” was organized. This workshop, chaired by F. De Proft, was organized under the auspicies of the International Solvay Institutes of Physics and Chemistry.   The organizing committee was composed of members of the Brussels Free Universities (Vrije Universiteit Brussel and Université Libre de Bruxelles) and Ghent University. The main aim of this workshop was to discuss past and present advances in the development, application and use of chemical concepts from quantum mechanics. It aimed at celebrating the achievements made in the field of conceptual quantum chemistry field by inviting the most prominent scientists that are active in this field but also at critically and thoroughly discussing the challenges ahead, among others the discussion whether these concepts still need to have an important place in contemporary quantum chemistry.

 

Since January 1, 2013 the ALGC resaerch group has been one of the Strategic Research Programs of the Vrije Universiteit Brussel.

 

REVIEW PAPERS


Overviews of the ALGC research can be found in:


- P. Geerlings, F. De Proft, W. Langenaeker, "Density Functional Theory : a source of chemical concepts and a cost-effective methodology for their calculation". Advances in Quantum Chemistry, 33, 303-328, (1999), Academic Press. Abstr.

- P. Geerlings, F. De Proft, " The HSAB Principle : Application of its Global and Local Forms in Organic Chemistry", Int. J. Quant. Chem., 80, 227 (2000). Abstr.

-F. De Proft, P. Geerlings, "Conceptual and Computational DFT in the study of Aromaticity", Chemical Reviews, Special Issue on Aromaticity, 101, 1451-1464, 2001. Abstr

- P. Geerlings, F. De Proft, "Chemical Reactivity as described by Quantum Chemical Methods", Int. J. Molec. Sci., 3 , 276 (2002) (freely available at the web). pdf

- F. De Proft, P. Geerlings, "Conceptual and Computational DFT as a Chemist's tool" in Recent Advances in Density Functional Methods, Part III, V. Barone, A. Bencini and P. Fantucci Editors, World Scientific Publishing Company, 2002, 137-167. Abstr.

- P. Geerlings, F. De Proft, R. Balawender, "The Nuclear Fukui function". Invited contribution to Reviews of Modern Quantum Chemistry, A Celebration to the Contributions of R.G. Parr, K.D. Sen Editor, World Scientific, Singapore, 1053-1070, 2002.

- P. Geerlings, F. De Proft, W. Langenaeker,
"Conceptual Density Functional Theory". Chemical Reviews, 103, 1793-1873, (2003). A general overview of the Conceptual DFT field.Abstr.

- P. Geerlings, F. De Proft, P.W. Ayers,
"Chemical Reactivity and the Shape Function". Invited Contribution to "Theoretical Aspects of Chemical Reactivity", Theoretical and
Computational Chemistry, Volume 16, A. Toro Labbé Editor, Elsevier Scientific Publishing Co., 2007, p 1-17 Abstr.

- P. Geerlings, F. De Proft,
"Conceptual DFT : the Chemical Relevance of Higher Order Response Functions".
PCCP,10, 3028, 2008 (Invited Paper) Abstr.

- F. De Proft, E. Chamorro, P. Perez, M. Duque, F. De Vleeschouwer, P. Geerlings,
"Spin Polarized Reactivity Indices from Density Functional Theory : Theory and Applications".
Invited Contribution to "Chemical Modelling : Applications and Theory", M. Springborg Editor, Specialist Periodical Report, RSC, 6, 63-111, 2009. Abstr.

- G. Roos, J. Messens, P. Geerlings,
"Enzymatic Catalysis : the emerging role of Conceptual DFT".
J. Phys. Chem. B. , 113, 13465, 2009 (review + cover) Abstr.

- A. Borgoo, P. Geerlings
Invited Contribution - Perspective "Information carriers and Information Theory in Quantum Chemistry."
PCCP, 13, 911, 2011 Abstr.

- P. A. Johnson, L.J. Bartolotti, P.W. Ayers, T. Fievez and P. Geerlings
"Charge density and chemical reactions: a unified view from Conceptual DFT."
Modern Charge-Density Analysis, C. Gatti and P. Macchi, Editors, Springer, 2012, 715-764. pdf

- A. Borgoo, M. Godefroid, P. Geerlings
"Atomic density functions: atomic physics calculations analyzed with methods from quantum chemistry." In Progress in Theoretical Chemistry and Physics, J. Maruani and S. Wilson Editors, Volume 22, part 4,p. 139-171, Springer-Verlag, 2011. Abstr.

- S. Bogatko, P. Geerlings,
"The Emerging Role of Quantum Chemistry in Environmental Science."
in "Progress on heavy metale in the Environment" B. Markert Editor (Book series: Progress in Environmental Science, Technology and Management. J. Nriagu series Editor) Maralte, p. 169-186 (2012) Abstr.

- P. Geerlings, P.W. Ayers, A. Toro Labbe, P.K. Chattaraj, F. De Proft,
"The Woodward Hoffmann rules regained by Conceptual Density Functional Theory".
Acc. Chem.Res.., 55, 683, 2012 Abstr.

- F. De Proft, P. W. Ayers, P. Geerlings,
"The Conceptual Density Functional Theory Perspective of Bonding."
" The Chemical Bond: Fundamental Aspects of Chemical Bonding.", Editors: G. Frenking and S. Shaik. Wiley, New York, Chapter 7, 233-265, 2014. ISBN: 978-3-527-33314-1 Abstr.

- P. Geerlings, S. Fias, Z. Boisdenghien, F. De Proft,
“Conceptual DFT: Chemistry from the Linear Response Function.”
Chem. Soc. Rev., 43, 4989, 2014 + Back Cover Abstr.

- F. De Vleeschouwer, P. Geerlings, F.De Proft,
"Property Optimizations with Bondary Conditions via the Best First Search Scheme." Cover Profile
Chem.Phys. Chem. , 17, 1414, 2016 Abstr + Cover

 


Complete list of ALGC publications.

 

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