FUNCTION GNTK(I,FR)
C     ===================
C
C     Hydrogenic bound-free Gaunt factor for the principal quantum
C     number I and frequency FR (from Klaus Werner)
C
      INCLUDE 'IMPLIC.FOR'
      GNTK=1.
      Y=1./FR      
      IF(I.EQ.1) THEN
         GNTK=0.9916+Y*(2.71852D13-Y*2.26846D30)
       ELSE IF(I.EQ.2) THEN
         GNTK=1.1050-Y*(2.37490D14-Y*4.07677D28)
       ELSE IF(I.EQ.3) THEN
         GNTK=1.1010-Y*(0.98632D14-Y*1.03540D28)
      END IF
      END