Multi-level computer simulations using orbital-free embedding formalism

Multi-level computer simulations

The the common element in methods known as multi-level computer simulations is the use of different basic physical descriptors of a complex investigated systems for different length- and/or time-scales. Our interest lies in methods, which use orbital-type of descriptors for a selected part of a larger system and simpler descriptors elswhere. The highest level is indispensabe to describe phenomena of essentialy quantum mechanical nature (chemical bonds, electronic spectroscopy).

Orbital-free embedding

We are especially interested in first-principles based description of the frontier between the subsystem described at the orbital level and its environment. A non-empirical formalism based on a mixed description of the whole system by means of embedded orbitals and electron density introduced in [T.A. Wesolowski and A. Warshel J. Phys. Chem. 97 (1993) 8050], which we refer to as: orbital-free embedding formalism, makes it possible to link the orbital-level description with any other type of theory provided it yields the electron density of the environment. In multi-level simulations based on this formalism, the embedded orbitals are obtained from Kohn-Sham-like equations (i.e. one-electron equations with a multiplicative effective potential). This effective embeding potential is expressed by means of the electron density in the environment. Any method, which yields the electron density as a function of position in space, can be used to generate the effective embedding potential.

Relation between orbital-free embedding and density-functional theory

Opposite to commonly used methods in quantum chemistry labeled as QM/MM or QM/MD, orbital-free embedding simulations do not involve any system-specific parameters because the effective embedding potential is expressed by means of universal density functionals. In the exact-functional limit, the orbital-free embedding formalism leads to the exact ground-state electron density. The results of practical orbital-free embedding calculations are not exact due to the use of approximate density functionals of the non-additive kinetic energy and exchange-correlation energy instead of the exact ones. Approximations to the bi-functional of the non-additive kinetic energy are also needed in subsystem formulation of density functional theory , whereas approximating the exchange-correlation energy is indispensable methods based on Kohn-Sham formulation. Our work on density functional theory focuses on studies of approximations to these functionals in order to improve the currently used ones and/or to determine their range of applicability. Currently, the approximate functionals allow us to study reliebly such embedded systems, which interact with their environment without forming covalent bonds.


Representative publications concerning multi-level computer simulations using the orbital-free embedding potential:


  • Multi-scale modelling of solvatochromic shifts from frozen-density embedding theory with non-uniform continuum model of the solvent: the coumarin 153

    Xiuwen Zhou, Jakub W. Kaminski, Tomasz A. Wesolowski Phys. Chem. Chem. Phys. , 13 (2011) 10565-10576 (special issue on Multilevel Modelling).

  • Modeling solvatochromic shifts using the orbital-free embedding potential at statistically-mechanically averaged solvent density

    Jakub W. Kaminski, Sergey Gusarov, Andriy Kovalenko, Tomasz A. Wesolowski Journal of Physical Chemistry A , 114 (2010) 6082.

  • One-electron Equations for Embedded Electron Density: Challenge for Theory and Practical Payoffs in Multi-Level Modeling of Complex Polyatomic Systems

    T.A. Wesolowski, Computational Chemistry: Reviews of Current Trends - Vol. 10 World Scientific, 2006, pp. 1-82.

  • Modeling solvent effects on electron spin resonance hyperfine couplings by frozen-density embedding.

    J. Neugebauer, M.J. Louwerse, P. Belanzoni, T.A. Wesolowski, E. J. Baerends, J. Chem. Phys. 123 (2005) 114101.

  • An Explicit Quantum Chemical Method for Modeling Large Solvation Shells Applied to Aminocoumarin C151

    J. Neugebauer, C.R. Jacob, T.A. Wesolowski, E.J. Baerends, J. Phys. Chem. A. 109 (2005) 7805.

  • The merits of the frozen-density embedding scheme to model solvatochromic shifts.

    J. Neugebauer, M.J. Louwerse, E.J. Baerends, T.A. Wesolowski, J. Chem. Phys. 122 (2005) 094115

  • Constraining the Electron Densities in DFT Method as an Effective Way for Ab Initio Studies of Metal-Catalyzed reactions.

    G. Hong, M. Strajbl, T.A. Wesolowski, and A. Warshel, J. Comput. Chem., 21 (2000) 1554.

  • Calculations of chemical processes in solution by density functional and other quantum mechanical techniques.

    R.P. Muller, T. Wesolowski, and A. Warshel, In: Density functional methods: Applications in chemistry and materials science., M. Springborg, ed. John Wiley and Sons, Ltd. (1997) pp.189-206

  • Ab-initio Frozen Density Functional Calculations of Proton Transfer Reactions in Solution.

    T.A. Wesolowski, R. Muller, and A. Warshel, J. Phys. Chem. 100 (1996) 15444.

  • Free Energy Perturbation Calculations of Solvation Free Energy Using Frozen Density Functional Approach.

    T.A. Wesolowski and A. Warshel, J. Phys. Chem. 98 (1994) 5183.

  • Frozen Density Functional Approach for ab-initio Calculations of Solvated Molecules.

    T.A. Wesolowski and A. Warshel J. Phys. Chem. 97 (1993) 8050.

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