Density functional theory study of phonons in graphene doped with Li, Ca and Ba Jelena Pešić, Vladimir Damljanović, Radoš Gajić, Kurt Hingerl and Milivoj Belić EPL, 112 6 (2015) 67006 Published online: 19 January 2016 DOI: 10.1209/0295-5075/112/67006