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Professor Michiel Sprik

Portrait of ms284

Computational physical chemistry

The broad area of the research activity in the group is computational physical chemistry. The main computational tool is Density Functional Theory based Molecular Dynamics (DFTMD or "Car-Parrinello"). Reactive species and the condensed phase environment are treated at strictly the same level of theory ("all-atom"). Using this fundamental approach we study reactivity in solutions, solids and at liquid/solid interfaces computing equilibrium constants, activation energies, electronic and vibrational spectra and other physical quantities such as dielectric properties. The DFTMD code we use is CP2K(http://www.cp2k.org) and occasionally also Quantum Espresso(http://www.quantum-espresso.org).

Interfacial electrochemistry

Computational electrochemistry is an application where all-atom DFTMD methods are particularly instructive and has become a major research topic for us. Our favourite model systems are the transition metal oxide electrodes used in energy conversion and storage. Proton coupled electron transfer (PCET) is a key process in these reactions. Unified treatment of oxidation/reduction and (de)protonation reactions is therefore crucial. Combining DFTMD and free energy perturbation (FTP) methods we have developed such a scheme. The central computational tool is reversible insertion of electrons and protons in periodic DFTMD model systems. Applying this method we can refer the computed redox free energies and electronic energy levels to the Standard Hydrogen Electrode (SHE) without having to introduce an additional interface with vacuum. We are using this approach to study the level alignment at electrochemical interfaces of typical transition metal oxides such as TiO2 and MnO2. The aim is to correlate the catalytic properties of the electrochemical interface to the electronic structure.

Figure: DFTMD model system of a TiO2 rutile (110) water interface at the point of zero net proton charge (PZC) consisting of 48 TiO2 units (Ti ions in yellow) and 71 H2O molecules in a periodically replicated orthorhombic MD cell (size 11.9 × 13.2 × 24.2 Å). The system has been reduced by inserting one electron and one proton. The excess electron visualized by the green spin density contours occupies a semilocalized orbital in the TiO2 slab. The proton is attached to the highlighted water molecule. The free energy of the double insertion gives the electron affinity of TiO2 (effectively the conduction band minimum) in contact with water relative to SHE.

 

Surface acidity and complexation

The surface of metal oxides exchanges protons with aqueous electrolytic solutions and binds also other ions. The excess surface charge is compensated by counterions in an electrical double layer. Surface acidity is therefore an important factor for the understanding of the reactivity. Since the solvation free energy of the proton is also the reference for acidity constants, the proton insertion method can be equally applied to compute the pKa of aqueous species in homogeneous solution as well as surfaces. We have used this method to compute surface pKa's of TiO2 and MnO2 and of main group oxides such as SiO2 (quartz) and Al(OH)3 (Gibbsite). Computational investigation of the properties of electric double layers and the effect on surface reactivity is a major challenge which is adressed in current research.

Publications

Identifying Trapped Electronic Holes at the Aqueous TiO2 Interface
J Cheng, J Vandevondele, M Sprik – Journal of Physical Chemistry C (2014) 118, 5437
Modeling the Oxygen Evolution Reaction on Metal Oxides: The Infuence of Unrestricted DFT Calculations
RV Mom, J Cheng, MTM Koper, M Sprik – Journal of Physical Chemistry C (2014) 118, 4095
Proton coupled electron transfer in water photo-oxidation at rutile TiO2(110) water interface
J Cheng, M Sprik – ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY (2013) 245
Acidity of edge surface sites of montmorillonite and kaolinite
X Liu, X Lu, M Sprik, J Cheng, EJ Meijer, R Wang – Geochimica et Cosmochimica Acta (2013) 117, 180
Hydration, acidity and metal complexing of polysulfide species: A first principles molecular dynamics study
X Liu, M Sprik, J Cheng – Chemical Physics Letters (2013) 563, 9
Solution structures and acidity constants of molybdic acid
X Liu, J Cheng, M Sprik, X Lu – Journal of Physical Chemistry Letters (2013) 4, 2926
Understanding surface acidity of gibbsite with first principles molecular dynamics simulations
X Liu, J Cheng, M Sprik, X Lu, R Wang – Geochimica et Cosmochimica Acta (2013) 120, 487
Vibrational sum frequency generation spectroscopy of the water liquid-vapor interface from density functional theory-based molecular dynamics simulations
M Sulpizi, M Salanne, M Sprik, M-P Gaigeot – Journal of Physical Chemistry Letters (2013) 4, 83
Alignment of electronic energy levels at electrochemical interfaces.
J Cheng, M Sprik – Physical chemistry chemical physics : PCCP (2012) 14, 11245
Oxide/water interfaces: how the surface chemistry modifies interfacial water properties.
MP Gaigeot, M Sprik, M Sulpizi – Journal of Physics: Condensed Matter (2012) 24, 124106
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Research Group

Research Interest Group

Telephone number

01223 336422 (fax)
01223 336314

Email address

ms284@cam.ac.uk