c this subroutine calculates unity vectors of a local reference system
c defined by atoms (i2), (i3), and (i4). the x axis is the axis from
c atom (i3) to atom (i2), and the xy plane is the plane defined by atoms
c this subroutine calculates unity vectors of a local reference system
c defined by atoms (i2), (i3), and (i4). the x axis is the axis from
c atom (i3) to atom (i2), and the xy plane is the plane defined by atoms