  The dynamics of electrons, spins and phonons induced by optical femtosecond
pulses has been simulated for the polaronic crystal
$\rm{Pr_{1/2}Ca_{1/2}MnO_3}$. The model used for the simulation has been
derived from first-principles calculations. The simulations reproduce the
experimentally observed melting of charge/orbital order with increasing
fluence. The loss of charge order in the high-fluence regime induces a
transition to a ferromagnetic metal. At low fluence, the dynamics is
deterministic and coherent phonons are created by the repopulation of
electronic orbitals, which are strongly coupled to the phonon degrees of
freedom. In contrast to the low-fluence regime, the magnetic transitions
occurring at higher fluence can be attributed to a quasi-thermal transition of
a cold-plasma-like state with hot electrons and cold phonons and spins. The
findings can be rationalized in a more complete picture of the electronic
structure that goes beyond the simple ionic picture of charge order.
