C     * MADELUNG POTENTIAL CALCULATIONS *
C     * ROCKSALT STRUCTURE *
      REAL*8    S,V,W,WI,WJ,WK
      INTEGER*4 I,J,K,N,M
C
      REWIND(20)
C
C     TAPE 20 = OUTPUT FILE
C
      PRINT *,'* MADELUNG POTENTIAL CALCULATIONS *'
      PRINT *,'* ROCKSALT STRUCTURE - 1 DIMENSIONAL*'
C
      WRITE(6,*) ('ENTER NUMBER OF POINTS:')
      READ(5,*) M
      V = 0.
      S = 0.
C
      DO 100 I=0,M
C     DO 99  J=0,M
C     DO 98  K=0,M
       WI=1.D+000
       IF (I.EQ.0) WI=0.5D+000
C      WJ=1.D+000
C      IF (J.EQ.0) WJ=0.5D+000
C      WK=1.D+000
C      IF (K.EQ.0) WK=0.5D+000
C      N=I+J+K
C      N=I+J
       N=I
       DUMMY = N/2.+0.1
C      IF (N.NE.(2*INT(DUMMY))) W=WI*WJ*WK
C      IF (N.EQ.(2*INT(DUMMY))) W=-WI*WJ*WK
C      IF (N.NE.(2*INT(DUMMY))) W=WI*WJ
C      IF (N.EQ.(2*INT(DUMMY))) W=-WI*WJ
       IF (N.NE.(2*INT(DUMMY))) W=WI
       IF (N.EQ.(2*INT(DUMMY))) W=-WI
       IF (N.NE.0) THEN
       S=S+W
C      V=V+W/DSQRT(DBLE(I*I+J*J+K*K))
C      V=V+W/DSQRT(DBLE(I*I+J*J))
       V=V+W/DSQRT(DBLE(I*I))
       ENDIF
C98    CONTINUE
C99    CONTINUE
100   CONTINUE
C
C     V=V*8.D+000
C     V=V*4.D+000
      V=V*2.D+000
      WRITE(6,*)
      WRITE(6,999) 'TOTAL CHARGE       : ',S
      WRITE(6,999) 'MADELUNG POTENTIAL : ',V
C      WRITE(20,999) 'TOTAL CHARGE       : ',S
C      WRITE(20,999) 'MADELUNG POTENTIAL : ',V
999   FORMAT(A21,D14.7)
      STOP
      END