Acoustic waves and phonon focus in Li crystal: the first principle study Hongzhi Fu, Liping Yao, Zhufeng Hou, Juan Fu and Yanming Ma Eur. Phys. J. B, 87 3 (2014) 76 Published online: 26 March 2014 DOI: 10.1140/epjb/e2014-40737-9