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allen-tildesley-book
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README,
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f.01,
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older-version
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********************************************************************************
** FICHE F.23. ROUTINE TO SET UP ALPHA FCC LATTICE OF LINEAR MOLECULES **
** This FORTRAN code is intended to illustrate points made in the text. **
** To our knowledge it works correctly. However it is the responsibility of **
** the user to test it, if it is to be used in a research application. **
********************************************************************************
SUBROUTINE FCC
COMMON / BLOCK1 / RX, RY, RZ, EX, EY, EZ
C *******************************************************************
C ** SETS UP THE ALPHA FCC LATTICE FOR N LINEAR MOLECULES. **
C ** **
C ** THE SIMULATION BOX IS A UNIT CUBE CENTRED AT THE ORIGIN. **
C ** N SHOULD BE AN INTEGER OF THE FORM ( 4 * ( NC ** 3 ) ), **
C ** WHERE NC IS THE NUMBER OF FCC UNIT CELLS IN EACH DIRECTION. **
C ** SEE FIGURE 5.10 FOR A DIAGRAM OF THE LATTICE AND A **
C ** DEFINITION OF THE FOUR ORIENTATIONAL SUBLATTICES. **
C ** **
C ** PRINCIPAL VARIABLES: **
C ** **
C ** INTEGER N NUMBER OF MOLECULES **
C ** REAL RX(N),RY(N),RZ(N) MOLECULAR POSITIONS **
C ** REAL EX(N),EY(N),EZ(N) UNIT VECTORS GIVING ORIENTATIONS **
C ** REAL RROOT3 1.0 / SQRT ( 3.0 ) **
C *******************************************************************
INTEGER N, NC
REAL RROOT3
PARAMETER ( NC = 3, N = 4 * NC ** 3 )
PARAMETER ( RROOT3 = 0.5773503 )
REAL RX(N), RY(N), RZ(N), EX(N), EY(N), EZ(N)
REAL CELL, CELL2
INTEGER I, IX, IY, IZ, IREF, M
C *******************************************************************
C ** CALCULATE THE SIDE OF THE UNIT CELL **
CELL = 1.0 / REAL ( NC )
CELL2 = 0.5 * CELL
C ** BUILD THE UNIT CELL **
C ** SUBLATTICE A **
RX(1) = 0.0
RY(1) = 0.0
RZ(1) = 0.0
EX(1) = RROOT3
EY(1) = RROOT3
EZ(1) = RROOT3
C ** SUBLATTICE B **
RX(2) = CELL2
RY(2) = CELL2
RZ(2) = 0.0
EX(2) = RROOT3
EY(2) = -RROOT3
EZ(2) = -RROOT3
C ** SUBLATTICE C **
RX(3) = 0.0
RY(3) = CELL2
RZ(3) = CELL2
EX(3) = -RROOT3
EY(3) = RROOT3
EZ(3) = -RROOT3
C ** SUBLATTICE D **
RX(4) = CELL2
RY(4) = 0.0
RZ(4) = CELL2
EX(4) = -RROOT3
EY(4) = -RROOT3
EZ(4) = RROOT3
C ** CONSTRUCT THE LATTICE FROM THE UNIT CELL **
M = 0
DO 99 IZ = 1, NC
DO 98 IY = 1, NC
DO 97 IX = 1, NC
DO 96 IREF = 1, 4
RX(IREF+M) = RX(IREF) + CELL * REAL ( IX - 1 )
RY(IREF+M) = RY(IREF) + CELL * REAL ( IY - 1 )
RZ(IREF+M) = RZ(IREF) + CELL * REAL ( IZ - 1 )
EX(IREF+M) = EX(IREF)
EY(IREF+M) = EY(IREF)
EZ(IREF+M) = EZ(IREF)
96 CONTINUE
M = M + 4
97 CONTINUE
98 CONTINUE
99 CONTINUE
C ** SHIFT CENTRE OF BOX TO THE ORIGIN **
DO 100 I = 1, N
RX(I) = RX(I) - 0.5
RY(I) = RY(I) - 0.5
RZ(I) = RZ(I) - 0.5
100 CONTINUE
RETURN
END
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