Multistate extrapolation of UVVis absorption spectra with QMQM

Multi-state extrapolation of UV/Vis absorption spectra with QM/QM hybrid methods Sijin Ren and Marco Caricato 6/21/2017 University of Kansas

Outline Ø Introduction Ø Multi-Scale and Multi-State Extrapolation of UV-Vis Spectra • • • Theory Implementation Application Ø Conclusion

Introduction Ø Theoretical simulations of UV/Vis absorption spectra of large chromophores Ø Important for the design of new compounds in solar cell development Ø More reliable methods may not be a�ordable in practical situations Ø Multi-scale or hybrid techniques Goal: obtain reliable spectra for compounds that are too large to be treated efficiently at a high level of theory

Why Multi-scale Methods? Ø Model large systems Ø Balance between accuracy and computational efficiency • Select regions • Select methods • Cap dangling bond

ONIOM Subtractive Multi-scale Methods Our own N-layered Integrated molecular Orbital molecular Mechanics 1 -4 Ø Accurately reproduce high level excitation energies and transition properties at a fraction of computational cost Ø Depends on the correct matching of states between the subcalculations 1. L. W. Chung, W. M. C. Sameera, R. Ramozzi, A. J. Page, M. Hatanaka, G. P. Petrova, T. V. Harris, X. Li, Z. Ke, F. Liu, H. -B. Li, L. Ding, and K. Morokuma, Chem. Rev 115, 5678 (2015). 2. M. Caricato, T. Vreven, G. W. Trucks, M. J. Frisch, and K. B. Wiberg, J. Chem. Phys. 131, 134105 (2009). 3. M. Caricato, T. Vreven, G. W. Trucks, and M. J. Frisch, J. Chem. Phys. 133 (2010). 4. M. Caricato, T. Vreven, G. W. Trucks, and M. J. Frisch, J. Chem. Theory Comput. 7, 180 (2011).

Method Overview Application of subtractive multi-scale methods on extrapolating UV-vis spectra Matching states among sub-calculations can be a challenging task Ø Extrapolate parameters: band position, band width, band height Ø Extrapolate many states at once Ø QM/QM extrapolation of UV-vis spectra S. Ren and M. Caricato, J. Chem. Phys. 144, 184102 (2016).

Calculated UV-vis Spectra Ø Extract excitation energy and oscillator strength from calculation Ø Assign a Gaussian function to each excitation Ø Sum all Gaussians together to form a spectrum

Implementation Details 1. Form separate spectra for sub-calculations (rl, mh, ml) 2. Locate peaks (position and height) on each spectrum 3. Locate band width parameter for each peak 4. Fit each band into a Gaussian 5. Check for existence of shoulder under each peak 6. Add Gaussian to describe shoulder 7. Locate Gaussian (position, width, and height) 8. Optimize the heights of shoulder and its main peak iteratively

Application of the Method Used: CAM-B 3 LYP/ 6 -311++G**(high level) B 3 LYP or CIS/ 6 -31+G*(low level)

Conclusion Ø Presented an approach for extrapolating UV-Vis spectra Ø Avoid the problem of matching individual states by extrapolating entire bands Ø This approach focuses on the main chromophoric moiety Ø Only bands that are included in all sub-calculations can be extrapolated Ø Better extrapolation with well defined chromophoric region S. Ren and M. Caricato, J. Chem. Phys. 144, 184102 (2016).

Acknowledgements Caricato Group Dr. Marco Caricato Dr. Alessandro Biancardi (Post Doc) Matthew Barclay Tal Aharon Amy Jystad Ty Balduf Hunter Leblanc

Thanks! Questions?