Involved in the biosynthesis of patchoulol. Produces also at least 13 additional sesquiterpene products, including alpha- and beta-patchoulene, alpha-bulnesene, seychellene, pogostol and alpha-guiaene. (2E,6E)-farnesyl diphosphate + H2O = diphosphate + patchoulol (2E,6E)-farnesyl diphosphate = alpha-guaiene + diphosphate (2E,6E)-farnesyl diphosphate = delta-guaiene + diphosphate Optimum pH is 7.0-7.5. Optimum temperature is 40 degrees Celsius. Secondary metabolite biosynthesis; terpenoid biosynthesis. Homodimer. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family.