The molecular structure of 1,3 lambda(4)delta(2),2,4-benzodithiadiazine (1) has been studied theoretically by a large number of computational methods. The results of calculations using different DFT functionals are compared with those obtained from HF, MP2, MP4(SDQ), QCISD and CCSD calculations. In addition, the influence of a number of basis sets on the calculated geometry was investigated. The results of the post-HF methods show that convergence of the geometrical parameters is already obtained for the relatively small 6-311+G* basis set. Taking the MP4(SDQ)/cc-pVTZ geometry as a reference the DFT/B1B95 functional appears to provide the most satisfactory description of all the examined functionals. (c) 2006 Elsevier B.V. All rights reserved.