  We provide insights into the atomistic details of the ultrafast
spatially-resolved breakdown of the insulating M1 phase in bulk VO2 employing
an ab initio technique based on time-dependent density-functional theory and
dynamical mean-field theory (DMFT-TDDFT). We find that the system is initially
metallized preferentially along the vanadium-dimer chains (CR axis), with a
subsequent growth of CR-elongated metallic bubbles. Moreover, we trace the
breakdown of the insulating phase to two types of oxygen atoms, resulting from
vanadium dimerization, which produce an unusual charge-density modulation in
the oxygen-atom chains with significant charge transfer to the inter-dimer
distance. These results are in qualitative agreement with experimental data and
shed light on the interplay between valence charge and lattice structure and
its role in the ultrafast response of strongly correlated insulators.
