obtaining the absorption and/or photodissociation cross section is a threefold challenge: computing the electronic potential energy surfaces, interpolating the potentials, and finding the cross section either by time-dependent or time-independent methods. We review electronic structure methods used for computing accurate potential energy surfaces for the electronic ground and accessible excited state as well as coupling between them (electronic transition dipole moments and diabatic coupling). Methods used for interpolation are discussed. The time-independent methods are based on the reflection principle and implicitly involve the short time approximation. in the time-dependent methods the time-dependent Schrodinger equation is solved exactly and the method considers the effect of dynamics away from the Franck-Condon region. We illustrate the presented methods using small molecules (HCl, N2O, OCS and HCHO) and their isotopic analogues.