QMC study of molecules for spintronics and photoswitching*

A combination of QMC and quantum chemistry (CAS-SCF) techniques are used to study two large molecules: azobenzene (AB) imporatnt as a photoswitch and vanadbenzene (VB), frequently used in spintronics [1]. In AB higher singlet state, S$_{2}$ the fingerprint of AB in excitation spectra has been calculated in addition to the low singlet states S and S$_{1}$ [2]. We have also calculated the lowest triplet T$_{1}$ vertical excitation, identified by EELS [3] as well as adiabatic T$_{1}$ excited state. All calculated energies are in excellent agreement with available experiments [3, 4]. In VB we focus initially on PES for dissociation and excited state of the vanadium cation. \\[4pt] [1] V.V. Maslyuk et al., Phys.Rev.Lett. 97, 201, (2006). [2] M. Dubecky et al., J.Chem.Phys, accepted (2010). [3] M. Allan, private communication. [4] J.-{\AA}. Andersson, R. Petterson, L. Tegn\'{e}r, J. Photochem. \textbf{20}, 17 (1982).