Abstract: The influence of the computation conditions on the results in the calculations with Kohn-Sham density functional theory has been studied through a series of calculations on the molecules with various compositions and structures such as BCl₃, SO₂, ZnO, TiCl₄, LuF₃. Three factors are considered. It is found that the completeness of the basis sets is the most important factor. The number of the grid points of the numerical integration is less important. The projection for decomposing the molecular charge into multipolar components centered in each atomic nucleus converges fairly rapidly. The molecular geometry and the fundamental vibrational frequency are insensitive to the computation conditions, while the total energy and bond energy are pretty sensitive. If the same basis set and the same numerical integration points are used for a molecule and its constituting atoms in calculating its bond energy, the error of the calculated result could be reduced. It is shown that the calculation results with an accuracy matched with the approximate DFTformulas can be obtained by choosing the mediate computation conditions with a smaller computational effort.

Key words: Density functional theory, Theoretical calculation, Bond energy, Bond length, Fundamental vibrational frequency