Clusters constitute an intermediate state of matter between molecules and solids. Physical and chemical properties of clusters, which range from sub-nanometer to about 1 micrometer, are size-dependent and thus tunable. This fact is of particular interest in materials science, catalysis and other fields of applied sciences such as nanoelectronics. The main goal of our research is to determine chemical properties, reactivity, composition and structure of metal clusters. We apply density functional calculations in several topics of cluster science: (1) Small isolated transition metal clusters and their compounds, which serve as reference systems in heterogeneous catalysis. (2) Studies of unique properties of isolated clusters in comparison to supported species. (3) Larger transition metal clusters, which have successfully been shown to act as reliable models for studying chemical reactions on solid state surfaces. (4) Ligand stabilized species like nickel carbonyl and gold thiolate clusters - beacuse of their usefulness as flexible and versatile building blocks in nanochemistry.
 A. Genest, A. Woiterski, S. Krüger, A. M. Shor, N. Rösch: The IMOMM (Integrated Molecular Orbitals/Molecular Mechanics) Approach for Ligand-Stabilized Metal Clusters. Comparison to Full Density Functional Calculations for the Model Thiolate Cluster Cu13(SCH2CH3)8, J. Chem. Theor. Comp. 2, 47-58 (2006); DOI 10.1021/ct050202r.
 I.V. Yudanov, K.M. Neyman, N. Rösch: Density Functional Study of Pd Nanoparticles with Subsurface Impurities of Light Element Atoms, Phys. Chem. Chem. Phys. 6, 116-123 (2004); DOI 10.1039/b311054k.
 K.M. Neyman, C.Inntam, A.B. Gordienko, I.V. Yudanov, N. Rösch: Adsorption of Carbon on Pd Clusters of Nanometer Size. A First-Principles Theoretical Study, J. Chem. Phys. 122, 174705, 1-9 (2005); DOI 10.1063/1.1888385.
 A. Del Vitto, L. Giordano, G. Pacchioni, N. Rösch: CO Adsorption on Ni4 and Ni8 Clusters Deposited on Regular and Defect Sites of the MgO (001) Surface, Surf. Sci. 575, 103-114 (2005); DOI 10.1016/j.susc.2004.11.019.
 A. Genest, S. Krüger, A.B. Gordienko, N. Rösch: Gold-Thiolate Clusters: A Relativistic Density Functional Study of the Model Species Au13(SR)n, R = H, CH3, n = 4, 6, 8, Z. Naturforsch. 59b, 1585-1599 (2004); PDF.
Systems composed of metal particles or metal films supported on an oxide are of immediate relevance for many applications, one of which is heterogeneous catalysis. Several years ago we initiated systematic computational studies of small d-metal particles deposited on the touchstone oxide support MgO using density functional (DF) cluster models. More recently we went on to apply an advanced cluster embedding method (EPE), which is one of the most accurate cluster model methods currently available, to investigate systematically the adsorption of 17 single d-metal atoms across the periodic table with the regular O2– sites on MgO(001) terraces as well as with Fs and Fs+ oxygen vacancies. These studies showed that, at variance with general belief, some d-metal atoms do not form stronger bound adsorption complexes with F-type surface defects than with regular sites and that metal atoms in M1/Fs complexes accumulate considerable amount of electron density, which governs the trend of the adsorption energies. We extended our studies of atoms on MgO(001) to larger metal particles. For instance, we addressed interactions of coinage metal dimers, trimers and tetramers with regular sites and O-vacancies on MgO(001). We have developed a time-dependent DFT tool in ParaGauss, which allows to calculate optical transitions in adsorbed systems. These transitions are believed to be characteristic of the adsorption species size, morphology, adsorption site and adsorption geomertry. Thus, theory can complement experimental studies in the interpretation of the results obtained for complex systems.
 I. Yudanov, G. Pacchioni, K. Neyman, N. Rösch: Systematic Density Functional Study of the Adsorption of Transition Metal Atoms on the MgO(001) Surface, J. Phys. Chem. B 101, 2786-2792 (1997); DOI 10.1021/jp962487x.
 K. M. Neyman, C. Inntam, V. A. Nasluzov, R. Kosarev, N. Rösch: Adsorption of d-metal atoms on the regular MgO(001) surface: Density functional study of cluster models embedded in an elastic polarizable environment, Appl. Phys. A 78, 823-828 (2004); DOI 10.1007/s00339-003-2437-5.
 K. M. Neyman, C. Inntam, A. V. Matveev, V. A. Nasluzov, N. Rösch: Single d-Metal Atoms on Fs and Fs+ Defects of MgO(001): A Theoretical Study across the Periodic Table, J. Am. Chem. Soc. 127, 11652-11660 (2005); DOI 10.1021/ja052437i.
 K. M. Neyman, Chan Inntam, L. V. Moskaleva, N. Rösch: Density Functional Embedded Cluster Study of Cu4, Ag4 and Au4 Species Interacting with Oxygen Vacancies on the MgO(001) Surface, Chem. Eur. J., 13, 277-286 (2007); DOI 10.1002/chem.200600545.