Ab initio molecular dynamics (AIMD) simulations were performed on the closed D-2h and open C-2v isomers of tetrasulfur After a careful calibration of the electronic structure method the calculations were done using the BPW91/aug-cc-pVTZ method This combination of method/basis set adequately reproduces the relative benchmark CCSD(T) energy difference [Matus M Dixon, D Peterson K A Harkless J A W Francisco J S J Chem Phys 2007, 127, 174305] between these two isomers and crucially, the fact that the D-2h structure is a transition state linking two equivalent (mirror images) C-2v isomers The trajectories show that the symmetric open C-2v isomers interconvert when passing through the D-2h closed transition state structure and that, unlike tetraoxygen, no three-dimensional structures arise The dynamic vibrational analysis yields peaks in good agreement with the static CCSD(T) harmonic frequencies and explains higher peaks as overtones thus showing that unlike previous AIMD DFT-based approaches carefully calibrated exchange-correlation functionals can produce reliable molecular dynamics results for complex PESs as the one corresponding to the lowest singlet of S-4