CODECS 2013 Workshop. San Lorenzo de El Escorial, Madrid, 18th –22nd April, 2013
Complex polarization propagator: a theoretical study of C6 dipoledipole dispersion coefficients and magnetic circular dichroism spectrum
for C60 fullerene.
Joanna Kauczor, Patrick Norman
Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping,
Sweden
[email protected]
Molecular properties for ground and excited states, and for transitions between these states,
can be determined from so-called molecular response functions and their poles and residues. In
standard response theory, absorption spectra are obtained from residues of response functions
and are therefore acquired by solving a generalized eigenvalue problem. This iterative procedure
starts from the energies of the lowest excited states, and only these lowest excitations are
addressed, meaning it may not be possible to access all excitation energies of interest using this
approach. The straightforward comparison between standard theory and experiment is therefore
impossible in many interesting regions of the spectrum, e.g. the X-ray absorption region. This
problem can be solved by using the complex polarization propagator approach (CPP), also
known as damped (complex) response theory.
A new algorithm for solving complex response equations has recently been developed,
namely: the algorithm with symmetrized trial vectors [1]. It is a subspace iterative algorithm that
combines fast convergence with a very efficient scheme of obtaining new trial vectors.
Calculations of dispersion coefficients [2], one-photon absorption, electronic circular dichroism,
magnetic circular dichroism (MCD) [3] and X-ray absorption spectra can be performed at the
Hartree-Fock and Kohn-Sham density functional level of theory with the current implementation
of the CPP solver in the DALTON program [4]. This has made it possible to perform calculations
on nanoparticles [5], which were out of reach of the previous solver.
Fig. 1. MCD spectrum of the C60 fullerene. The inset shows the experimental MCD and absorption spectra
taken from Gasyna et al. [6]
References
1. J. Kauczor, P. Jørgensen and P. Norman, J. Chem. Theory Comput., 7, 1610 (2011).
2. J. Kauczor, P. Norman and W. A. Saidi, accepted in J. Chem. Phys.
3. T. Fahleson, J. Kauczor, P. Norman and S. Coriani, accepted in Mol. Phys.
4. DALTON, a molecular electronic structure program, Release: Dalton2013 (2013).
5. M. Ahrén, L. Selegård, F. Söderlind, M. Linares, J. Kauczor, P. Norman, P.-O. Käll and K. Uvdal, J.
Nanopart. Res., 14, 1006 (2012).
6. Z. Gasyna, P. N. Schatz, J. P. Hare, T. J. Dennis, H. W. Kroto, R. Taylor and D. R. M. Walton, Chem.
Phys. Lett., 183, 283 (1991).