Density functional theory calculation of electron spectra of formaldehyde

Both ionization and excitation spectra for outer valence-shell electrons and inner-shell electrons of formaldehyde are calculated with density functional methods. In addition, both resonant and non-resonant X-ray emission spectra are also computed. For all of these calculations, we use four different basis sets: large and efficient sets, with and without diffuse functions. Choice of method for each type of electron spectroscopy is based on past experience. For excitation spectra, especially when the final states are Rydberg-like in nature, basis sets with diffuse functions are recommended. On the other hand, for ionization spectra and X-ray emission spectra, diffuse functions are apparently unnecessary. Available experimental data for formaldehyde enable us to judge the accuracy of the present density functional calculations. The average absolute deviation from experiment is generally about 0.3 eV or better, confirming the adequacy of our choice of method.