c atom (i3) to atom (i2), and the xy plane is the plane defined by atoms
c (i2), (i3), and (i4). z axis is directed according to the sign of the
c vector product (i3)-(i2) and (i3)-(i4). sets fail to .true. if atoms
c atom (i3) to atom (i2), and the xy plane is the plane defined by atoms
c (i2), (i3), and (i4). z axis is directed according to the sign of the
c vector product (i3)-(i2) and (i3)-(i4). sets fail to .true. if atoms