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The electronic structure and chemical bonding of AnF4(An=Th to Cm)are investigated under constraint of tetrahedral(Td)symmetry by using scalar relativistic density functional theory(DFT).The An-F bond length decreases along the series in consistent with the actinide contraction trend.Extensive bond order analyses show a relatively stronger An-F bond for An=U,Np and a weaker one for An=Th,Am and Cm.The An-F symmetric stretching vibrational frequencies of AnF4 also support this trend of An-F bond strength.The overlap integral of F 2p group orbitals and actinide 5f,6d orbitals and Morokuma-Ziegler type energy decomposition analysis(EDA)indicate the considerable covalent interaction in An-F bonding in spite of its dominant ionic character.The molecular orbital energy levels of AnF4 show that the 5f orbitals of An(Th-Cm)come into closer in energy to F 2p based orbitals,which allows greater orbital mixing of metal and ligand,thus leading to increasing 5f component in Mulliken population.Natural population analysis indicates that the covalency of An-F bond increases initially before decreasing in the latter systems with a maximum at Np and Pu.Electron density analyses by using topological quantum methodologies,atom in molecule(AIM)and electron localization function(ELF),have also been carried out,and the results shows the highly ionic character in An-F bonds with weak covalent interaction,and particularly low covalence in AmF4 and CmF4,also in good agreement with the above EDA and population analysis results.Compared to the tetravalent actinide organic-ligand compound AnCp4(An = Th-Cm; Cp = η5-C5H5)reported in the literature,our study on AnF4 indicates a much more prominent actinide-ligand covalent interaction.