Atomistic spin dynamics (ASD) simulations of ultrafast demagnetization in ferromagnetic iron and cobalt. The ASD simulations here are energy-conserving, which means that energy flow into and out of the spin system is considered. The dataset contains simulations at four different pump laser fluences for iron and six different fluences for cobalt. The excitation was assumed to be homogeneous throughout the simulated volume. The heat capacities and electron-phonon coupling parameters which were used in the ASD simulations are provided in the folder "heat capacities and G_ep". More information is available here: - https://arxiv.org/abs/2110.00525 - Zahn et al. Phys. Rev. Research 3, 023032 (2021) https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.3.023032