--- /dev/null
+ subroutine refsys(i2,i3,i4,e1,e2,e3,fail)
+ implicit real*8 (a-h,o-z)
+ include 'DIMENSIONS'
+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 (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 (i2) and (i3) or (i3) and (i4) coincide or atoms (i2), (i3), and (i4)
+c form a linear fragment. returns vectors e1, e2, and e3.
+ logical fail
+ double precision e1(3),e2(3),e3(3)
+ double precision u(3),z(3)
+ include "COMMON.CHAIN"
+ data coinc /1.0d-13/,align /1.0d-13/
+ fail=.false.
+ s1=0.0d0
+ s2=0.0d0
+ do 1 i=1,3
+ zi=c(i,i2)-c(i,i3)
+ ui=c(i,i4)-c(i,i3)
+ s1=s1+zi*zi
+ s2=s2+ui*ui
+ z(i)=zi
+ 1 u(i)=ui
+ s1=sqrt(s1)
+ s2=sqrt(s2)
+ if (s1.gt.coinc) goto 2
+ write (iout,1000) i2,i3,i1
+ fail=.true.
+ return
+ 2 if (s2.gt.coinc) goto 4
+ write(iout,1000) i3,i4,i1
+ fail=.true.
+ return
+ 4 s1=1.0/s1
+ s2=1.0/s2
+ v1=z(2)*u(3)-z(3)*u(2)
+ v2=z(3)*u(1)-z(1)*u(3)
+ v3=z(1)*u(2)-z(2)*u(1)
+ anorm=sqrt(v1*v1+v2*v2+v3*v3)
+ if (anorm.gt.align) goto 6
+ write (iout,1010) i2,i3,i4,i1
+ fail=.true.
+ return
+ 6 anorm=1.0/anorm
+ e3(1)=v1*anorm
+ e3(2)=v2*anorm
+ e3(3)=v3*anorm
+ e1(1)=z(1)*s1
+ e1(2)=z(2)*s1
+ e1(3)=z(3)*s1
+ e2(1)=e1(3)*e3(2)-e1(2)*e3(3)
+ e2(2)=e1(1)*e3(3)-e1(3)*e3(1)
+ e2(3)=e1(2)*e3(1)-e1(1)*e3(2)
+ 1000 format (/1x,' * * * error - atoms',i4,' and',i4,' coincide.')
+ 1010 format (/1x,' * * * error - atoms',2(i4,2h, ),i4,' form a linear')
+ return
+ end