Scientific Calendar Event

A new algorithm to solve the TDDFT equations in the space of the density fitting auxiliary basis set has been developed and implemented in ADF.1 The TDDFT equations are recast to a non-homogeneous linear system, whose size is much smaller than in Casida formulation, allowing to calculate a wide portion of the absorption spectrum for large systems. The method extracts the spectrum from the imaginary part of the polarizability at any given photon energy, avoiding the bottleneck of Davidson diagonalization. The original idea which made the present scheme very efficient consists in the simplification of the double sum over occupied-virtual pairs in the definition of the dielectric susceptibility, which allows an easy calculation of such matrix as a linear combination of constant matrices with photon energy dependent coefficients. The method has been applied to very different systems in nature and size (from H2 to [Au309]-)2,3. In all cases, the maximum deviations found for the excitation energies with respect to Casida approach are below 0.2 eV. The new algorithm has the merit to calculate the spectrum at whichever photon energy but also to allow a deep analysis of the results, in terms of Transition Contribution Maps,4 plasmon scaling factor analysis5, induced density analysis, and with a fragment projection analysis6. Circular Dichroism of large systems becomes also affordable.7

1.O. Baseggio, G. Fronzoni and M. Stener, J. Chem. Phys., 2015, 143, 024106.
2. O. Baseggio, M. De Vetta, G. Fronzoni, M. Stener, L. Sementa, A. Fortunelli and A. Calzolari, J. Phys. Chem. C, 2016, 120, 12773.
3. A. Fortunelli, L. Sementa, V. Thanthirige, T. Jones, M. Stener, K. Gagnon, A. Dass, G. Ramakrishna, J. Phys. Chem. Lett, 2017, 8, 457.
4. S. Malola, L. Lehtovaara, J. Enkovaara and H. Häkkinen, ACS Nano 2013, 7, 10263.
5. S. Bernadotte, F. Evers, C. R. Jacob, J. Phys. Chem. C 2013, 117, 1863.
6. L. Sementa, G. Barcaro, O. Baseggio, M. De Vetta, A. Dass, E. Aprà, M. Stener, A. Fortunelli, J. Phys. Chem. C submitted.
7. O. Baseggio, D. Toffoli, G. Fronzoni, M. Stener, L. Sementa, A. Fortunelli J. Phys. Chem. C, 2016, 120, 24335.
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