Dihedral angle convention is inverted

[tfgg]

Comparison of tests to JMol seems to get opposite sign. JMol uses the correct convention, which is (according to David):

"The convention for dihedral angles is that as you look down the B-C bond in a A-B-C-D system with A at 0 deg., a positive number is assigned to the dihedral where C is at 0-180 deg. in a clockwise direction. A negative is assigned if C is at 0-180 in the anticlockwise direction. In most software the value of the dihedral is not restricted, so if you assign an angle of +270 deg. it'll understand this as -90. Here's how IUPAC describe it: http://goldbook.iupac.org/T06406.html"

The sign should be inverted in the current code.