In this talk I will mainly discuss first-principles modeling of spins in organic semiconductors and molecules. Transition-metal phthalocyanines, as common organic semiconductors, have been found to have a huge potential for molecular spintronics and quantum computing. Recent cutting-edge density-functional theory calculations, combined with state-of-the-art magnetic measurements, showed that there is a large exchange constant in cobalt-phthalocyanines [1,2], which is higher than the boiling point of liquid nitrogen. This research illustrates the potential of cobalt-phthalocyanines for organic spintronics and quantum information processing. In addition, I will show that electron spin resonance simulations can be used for studying the nano-structures of organic materials . Following this, from the perspective of quantum information processing, I will show that the radical-triplet pair could have the potential for the control of the creation of interaction, thus quantum gate operations entangling spins in molecules. This will be illustrated based on a set of first-principles calculations and spin-detection experiments and simulations [4,5].
 High temperature anti-ferromagnetism in a molecular semiconductor, Michele Serri, Wei Wu, L. Fleet, N. M. Harrison, C. W. Kay, A. J. Fisher, C. Hirjibehedin, G. Aeppli, S. Heutz, Nat. Commun. 5, 3079 (2014).
 Electronic structure and magnetic properties of cobalt phthalocyanine, Wei Wu, N. M. Harrison, and A. J. Fisher, Phys. Rev. B 88, 024426 (2013).
 Spin-based diagnostics of nanostructure in films of a common molecular semiconductor, M. Warner, S. Mauthoor, S. Felton, Wei Wu, J. A. Gardener, S. Din, D. Klose, G. W. Morley, A. M. Stoneham, A. J. Fisher, G. Aeppli, C. W. M. Kay, and S. EM Heutz, ACS Nano 6, 10808 (2012).
 Y. Teki, S. Miyamoto, K. Iimura, M. Nakatsuji, and Y. Miura, J. Am. Chem. Soc. 122, 984 (2000).
 Phenomenological modelling for time-resolved electron paramagnetic resonance in radical-triplet system, arXiv: 1501.00316 (2015).