We have studied metal complexation with (amino)polycarboxylic acid ligands using density functional methods. Geometry optimisations, continuum-solvation model (COSMO), mixed cluster-continuum model, and Car-Parrinello molecular dynamics simulations have been carried out. The metal solvation energies for Mg2+, Ca2+, Mn2+, Fe3+, and Zn 2+, and their complexation energies with seven (amino)polycarboxylic acid-ligands (total charges between -6 and -4) have been calculated. The solvation energies are not very accurate. The complexation energies with ligands are overestimated, but the trends are reproduced correctly. An effective parametrisation is introduced to correct for omitted contributions to energies. Explicit calculation of these corrections is discussed. The effective parametrisation results in an easy to use and fast procedure to estimate the metal ion complexation constant with different ligands.