One goal of a computational investigation is thus to determine ΔH, ΔS and ∆𝐺 r for a set of ALD reactions. As a first approximation, the reaction energy (ΔEr) is often used instead of ΔGr. These electronic energies result directly from ab initio computations and neglect zero-point vibrational energy, temperature and pressure effects (T = 0 K, p = 0 bar). This approximation must be used with care in ALD modelling due to the elevated temperatures and low pressures which can both affect the entropy contribution strongly. The common approach to move from ∆𝐸 r to ∆𝐺 r is the rigid-rotor harmonic oscillator (RRHO) approximation which is rooted in statistical thermodynamics. This approach introduces efficient approximations for translational (trans), rotational (rot), vibrational (vib), and electronic (elec) contributions to H and S (eq. 1.3, eq. 1.4).