The octadecane dimer (CBH, Figure ) offers a striking example. Without MBD, PBE density barely captures weak vdW attraction between chains, while small repulsive contacts between hydrogens are completely missed. These repulsive interactions appear with PBE+MBD, along with stronger, more widespread vdW attractions. Hydrogen bonds are also better resolved with MBD, as seen in C3GC and DNA-ellipticine.