Understanding (and possibly solving) chemical problems, especially of industrial relevance, is our main activity. To this end we use the armory of tools known as computational chemistry. The areas of interest span from understanding structure and function relationship in organometallic compounds, to unraveling the mechanistic of catalysts at work, to soft condensed matter simulations. Finally, we are not shy to tackle systems of biological interest. In all cases we try to interact as much as possible with experimentalists. Often we are unsatisfied with the available tools and/or models and we develop new ones. Particular interest is devoted to development of methods for modelling systems across time and length scales.

Hybrid Quantum Mechanical Molecular Mechanics Methods.

In collaboration with the group of Tom Ziegler, we have been deeply involved in the development of hybrid QM/MM methods within the ADF package. QM/MM approaches are of remarkable relevance since they allow to work on real size systems. That is, no reduction of the system to an oversimplified and chemically poorly relevant model is needed

Dispersion interaction within DFT.

We are working to implement a modified version of Grimme’s approach to include dispersion interaction within DFT.

Calculation of solvent accessible surface areas.

In collaboration with a bioinformatics group we developed a tool for the fast calculation of solvent accessible surface areas of proteins and nucleic acids, POPS, that works at atomic level and at coarse grained level.

Ion-pairing in Organometallics.

Recently, we have developed a protocol, based on a classical Molecular Dynamics approach, to study organometallic ion pairs in low polarity solvents, see Figure.

Schematic representation of the system used to simulate a metallocenium ion-pair in benzene solution.

Force-Fields for common organic solvents: Benzene and Cyclohexane.

We investigated mixtures of cyclohexane and benzene by means of all-atom molecular dynamics simulations. The force fields have been validated calculating thermodynamic properties such as density and enthalpy of mixing and diffusion coefficient for five different compositions of benzene/cyclohexane mixtures and compared with experimental results.

Calculated and experimental enthalpies of mixing (kJ/mol). The value of enthalpy of mixing obtained using a different force field for the 1:1 mixture is also reported.

References
1) Giuseppe Milano, Florian Mueller-Plathe, "Cyclohexane-Benzene Mixtures: Thermodynamics and Structure from Atomistic Simulations", J. Phys. Chem. B, 2004, 108, 7415.

Polymer Coarse-Graining.

High molecular weight polymer chains are difficult to relax. The longest relaxation of an entangled polymer melt of length N scales at least as N³, giving at least N⁴ in cpu time, this way is only feasible for relatively short chain lengths. One way to circumvent this problem is to reduce the degrees of freedom by coarsening the models and keeping only those degrees of freedom that are deemed relevant for the particular range of interest. Recently, in collaboration with Florian Mueller-Plathe (TU-Darmstadt, Germany) we developed new tools and models in the framework of systematic polymer coarse-graining. The main point of this class of methods is the mapping of atomistic features to mesoscopic models. To this end, one groups several atom together into “super-atoms”.

Mesoscale Potentials: we introduced a new class of mesoscale potentials based on sum of Gaussian functions. A multipeaked distribution of a structural parameter q can be approximated by a sum of n Gaussian functions characterized by their centres (q_ci), total area (A_i) and width (w_i):

   (1)

Given a distribution P(q) of some structural parameter q such as a bond length or an angle, a first approximation of the corresponding potential can be derived doing a simple Boltzmann inversion of P(q). The corresponding potential obtained by Boltzmann inversion can be written as:

(2)

If we define , the potential and the corresponding expression for the force can be written in a more compact form:

 (3)                                                                                   (4)

For the bond potentials it is possible to derive equations similar to eq. 3 and eq. 4 for potential and forces, respectively.

References
1) Giuseppe Milano, Sylvain Goudeau, Florian Mueller-Plathe, "Multicentred Gaussian-Based Potentials for Coarse-Grained Polymer Simulations: Linking Atomistic and Mesoscopic Scales", J. Polymer. Science Part B: Polymer Physics, 2005, 43, 87.

Realistic Models of Vinyl Polymers: we introduced a systematic procedure to coarse-grain atomistic models of the largest family of synthetic polymers into a mesoscopic model that is able to keep detailed information about chain stereosequences. The mesoscopic model consists of sequences of superatoms centered on methylene carbons of two different types according to the kind of diad (m or r) they belong to. The proposed mesoscale model has been successfully tested against structural and dynamical properties for different chain lengths and opens the possibility of relaxing melts of high molecular weight vinyl polymers.

a) Polystyrene m and r diads in transplanar conformation (hydrogen atoms on phenyl rings are omitted for clarity). b) Illustration of the mapping scheme for polystyrene:one bead corresponds to a diadic m or r unit. The center of these super-atoms, as indicated by filled squares, are the methylene carbons.

Histograms (at 500 K) of a) r-r-r; b) r-m-r ;angle extracted from atomistic (empty circles) and from coarse-grained simulations (solid lines). Interchain c) m-m ; d) r-r  pair correlation function from atomistic simulations (empty circles) and obtained with the coarse grained model (solid lines). e)Values of gyration radii obtained by simulations of polystyrene coarse grained models (■), as function of molecular weight, in comparison with available experimental data (Δ SANS data from melts, ○ light scattering data from -solutions ) are reported.

References
1) Giuseppe Milano, Florian Mueller-Plathe, "Mapping Atomistic Simulations to Mesoscopic Models: A Systematic Coarse-Graining Procedure for Vinyl Polymer Chains", J. Phys. Chem. B , 2005, 109, 18609.

Reverse-Mapping: systematic procedures to obtain well relaxed atomistic melt structures from mesocale models are important tools to obtain reliable and detailed models of polymers in bulk.

A fast and efficient reverse-mapping procedure, successfully tested against experimental data, allows to obtain atomistic models of both stereoregular and stereoirregular polymers and opens the possibility of relaxing large molecular weight melts of vinyl chains.

The mesocale and the reconstructed atomistic models of a 350-mer chains of atactic polystyrene. The read beads are the meso and the yellow ones the racemo superatoms.

References
1) Giuseppe Santangelo, Andrea Di Matteo, Florian Müller-Plathe and Giuseppe, "MilanoFrom Mesoscale back to Atomistic Models: A Fast Reverse-Mapping Procedure for Vinyl Polymer Chains", Submitted

Automatic Optimization of Force-Fields.

Fast generation of accurate force fields without the frustrations of parameterisation by hand. We developed a fast and accurate method and the relative software for automatic optimization of point charges from ab-initio calculations.