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mc-dumbbell.f
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mc-dumbbell.f
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********************************************************************************
** FICHE F.16. HARD DUMB-BELL MONTE CARLO PROGRAM **
** 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. **
********************************************************************************
PROGRAM MCBELL
COMMON / BLOCK1 / RX, RY, RZ, EX, EY, EZ
C *******************************************************************
C ** CONSTANT-NVT MONTE CARLO PROGRAM FOR HARD DUMB-BELLS. **
C ** **
C ** THE BOX IS OF UNIT LENGTH, -0.5 TO +0.5. THERE ARE NO LOOKUP **
C ** TABLES INCLUDED. **
C ** **
C ** PRINCIPAL VARIABLES: **
C ** **
C ** INTEGER N NUMBER OF MOLECULES **
C ** INTEGER NATOM NUMBER OF ATOMS PER MOLECULE **
C ** INTEGER NSTEP MAXIMUM NUMBER OF CYCLES **
C ** INTEGER IPRINT PRINT INTERVAL **
C ** INTEGR ISAVE SAVE INTERVAL **
C ** INTEGER IRATIO MAX DISPLACEMENT UPDATE INTERVAL **
C ** REAL RX(N),RY(N),RZ(N) POSITIONS **
C ** REAL EX(N),EY(N),EZ(N) ORIENTATIONS, UNIT AXIAL VECTOR **
C ** REAL DAB(NATOM) DISTANCE FROM COM TO NATOM **
C ** REAL D REDUCED BOND LENGTH (D/SIGMA) **
C ** REAL DENS REDUCED DENSITY **
C ** REAL SIGMA HARD SPHERE DIAMETER **
C ** REAL DRMAX REDUCED MAXIMUM DISPLACEMENT **
C ** REAL DOTMIN CONTROLS ANGULAR DISPLACEMENT **
C ** LOGICAL OVRLAP TRUE IF DUMBBELLS OVERLAP **
C ** **
C ** ROUTINES REFERENCED: **
C ** **
C ** SUBROUTINE CHECK ( SIGMA, DAB, OVRLAP ) **
C ** CHECKS FOR OVERLAPS IN A FLUID OF HARD DUMBELLS **
C ** SUBROUTINE ORIEN ( EXIOLD, EYIOLD, EZIOLD, DOTMIN, EXINEW, **
C ** : EYINEW, EZINEW ) **
C ** PRODUCES A TRIAL RANDOM ORIENTATION FOR A MOLECULE **
C ** REAL FUNCTION RANF( DUMMY ) **
C ** RETURNS A UNIFORM RANDOM NUMBER BETWEEN ZERO AND ONE **
C ** SUBROUTINE READCN ( CNFILE ) **
C ** READS IN A CONFIGURATION **
C ** SUBROUTINE TEST ( RXI, RYI, RZI, I, EXI, EYI, EZI, SIGMA, **
C ** : DAB, OVRLAP ) **
C ** CHECKS FOR OVERLAPS AFTER THE DISPLACEMENT OF MOLECULE I **
C ** SUBROUTINE WRITCN ( CNFILE ) **
C ** WRITES OUT A CONFIGURATION **
C *******************************************************************
INTEGER N, NATOM
PARAMETER ( N = 108, NATOM = 2 )
REAL RX(N), RY(N), RZ(N), EX(N), EY(N), EZ(N)
REAL DAB(NATOM), DRMAX, DOTMIN, DENS, D, SIGMA, RATIO
REAL RXIOLD, RYIOLD, RZIOLD, RXINEW, RYINEW, RZINEW
REAL EXIOLD, EYIOLD, EZIOLD, EXINEW, EYINEW, EZINEW
REAL RANF, DUMMY, ACM, ACMMVA
INTEGER STEP, I, NSTEP, IRATIO, IPRINT, ISAVE
LOGICAL OVRLAP
CHARACTER TITLE*80, CNFILE*80
C *******************************************************************
C ** READ INPUT DATA **
WRITE(*,'(1H1,'' **** PROGRAM MCBELL **** '')')
WRITE(*,'(/ '' CONSTANT-NVT MONTE CARLO '')')
WRITE(*,'( '' FOR HARD DUMBELLS ''/)')
WRITE(*,'('' ENTER THE RUN TITLE '')')
READ (*,'(A)') TITLE
WRITE(*,'('' ENTER NUMBER OF CYCLES '')')
READ (*,*) NSTEP
WRITE(*,'('' ENTER NUMBER OF CYCLES BETWEEN OUTPUT '')')
READ (*,*) IPRINT
WRITE(*,'('' ENTER NUMBER OF CYCLES BETWEEN DATA SAVES '')')
READ (*,*) ISAVE
WRITE(*,'('' ENTER INTERVAL FOR UPDATE OF MAX. DISPL. '')')
READ (*,*) IRATIO
WRITE(*,'('' ENTER THE CONFIGURATION FILE NAME '')')
READ (*,'(A)') CNFILE
WRITE(*,'(/'' ENTER THE FOLLOWING IN LENNARD-JONES UNITS '',/)')
WRITE(*,'('' ENTER THE DENSITY '')')
READ (*,*) DENS
WRITE(*,'('' ENTER THE MAXIMUM DISPLACEMENT '')')
READ (*,*) DRMAX
WRITE(*,'('' ENTER THE REDUCED BOND LENGTH '')')
READ (*,*) D
C ** WRITE INPUT DATA **
WRITE(*,'( //1X ,A )') TITLE
WRITE(*,'('' NUMBER OF ATOMS '',I10 )') N
WRITE(*,'('' NUMBER OF CYCLES '',I10 )') NSTEP
WRITE(*,'('' OUTPUT FREQUENCY '',I10 )') IPRINT
WRITE(*,'('' SAVE FREQUENCY '',I10 )') ISAVE
WRITE(*,'('' RATIO UPDATE FREQUENCY '',I10 )') IRATIO
WRITE(*,'('' CONFIGURATION FILE NAME '',A )') CNFILE
WRITE(*,'('' DENSITY '',F10.5 )') DENS
WRITE(*,'('' MAX. DISPLACEMENT '',F10.5 )') DRMAX
WRITE(*,'('' BOND LENGTH '',F10.5 )') D
C ** SET DEPENDENT VARIABLES **
SIGMA = ( DENS / REAL ( N ) ) ** ( 1.0 / 3.0 )
DAB(1) = D * SIGMA / 2.0
DAB(2) = - DAB(1)
DRMAX = DRMAX * SIGMA
DOTMIN = 0.2
C ** WRITE OUT SOME USEFUL INFORMATION **
WRITE( *, '( '' NUMBER OF MOLECULES = '', I10 )' ) N
WRITE( *, '( '' NUMBER OF ATOMS = '', I10 )' ) NATOM
WRITE( *, '( '' SIGMA / BOX = '', F10.5 )' ) SIGMA
WRITE( *, '( '' DAB(1) / BOX = '', F10.5 )' ) DAB(1)
WRITE( *, '( '' DAB(2) / BOX = '', F10.5 )' ) DAB(2)
WRITE( *, '( '' DRMAX / BOX = '', F10.5 )' ) DRMAX
WRITE( *, '( '' DOTMIN = '', F10.5 )' ) DOTMIN
C ** READ IN INITIAL CONFIGURATION **
CALL READCN ( CNFILE )
C ** CHECK FOR OVERLAPS IN INITIAL CONFIGURATION **
CALL CHECK ( SIGMA, DAB, OVRLAP )
IF ( OVRLAP ) STOP 'OVERLAP IN INITIAL CONFIGURATION'
C ** ZERO ACCUMULATORS **
ACM = 0.0
ACMMVA = 0.0
WRITE( *, '(//'' START OF MARKOV CHAIN ''//)')
WRITE( *, '( '' ACM RATIO DRMAX DOTMIN '')')
C *******************************************************************
C ** LOOP OVER CYCLES BEGINS **
C *******************************************************************
DO 100 STEP = 1, NSTEP
C ** LOOP OVER MOLECULES **
DO 99 I = 1, N
RXIOLD = RX(I)
RYIOLD = RY(I)
RZIOLD = RZ(I)
EXIOLD = EX(I)
EYIOLD = EY(I)
EZIOLD = EZ(I)
C ** MOVE I AND PICKUP THE CENTRAL IMAGE **
RXINEW = RXIOLD + ( 2.0 * RANF ( DUMMY ) - 1.0 ) * DRMAX
RYINEW = RYIOLD + ( 2.0 * RANF ( DUMMY ) - 1.0 ) * DRMAX
RZINEW = RZIOLD + ( 2.0 * RANF ( DUMMY ) - 1.0 ) * DRMAX
RXINEW = RXINEW - ANINT ( RXINEW )
RYINEW = RYINEW - ANINT ( RYINEW )
RZINEW = RZINEW - ANINT ( RZINEW )
C ** CHANGE THE ORIENTATION OF MOLECULE I **
CALL ORIEN ( EXIOLD, EYIOLD, EZIOLD, DOTMIN,
: EXINEW, EYINEW, EZINEW )
C ** CHECK FOR ACCEPTANCE **
CALL TEST ( RXINEW, RYINEW, RZINEW, I,
: EXINEW, EYINEW, EZINEW, SIGMA, DAB, OVRLAP )
IF ( .NOT. OVRLAP ) THEN
C ** ACCEPT MOVE **
RX(I) = RXINEW
RY(I) = RYINEW
RZ(I) = RZINEW
EX(I) = EXINEW
EY(I) = EYINEW
EZ(I) = EZINEW
ACMMVA = ACMMVA + 1.0
ENDIF
ACM = ACM + 1.0
99 CONTINUE
C ****************************************************************
C ** LOOP OVER MOLECULES COMPLETE **
C ****************************************************************
C ** PERFORM PERIODIC OPERATIONS **
C ** CHANGE MAXIMUM DISPLACEMENT **
IF ( MOD ( STEP, IRATIO ) .EQ. 0 ) THEN
RATIO = ACMMVA / REAL ( N * IRATIO )
IF ( RATIO .GT. 0.5 ) THEN
DRMAX = DRMAX * 1.05
DOTMIN = DOTMIN * 1.025
ELSE
DRMAX = DRMAX * 0.95
DOTMIN = DOTMIN * 0.975
ENDIF
ACMMVA = 0.0
ENDIF
C ** WRITE OUT RUNTIME INFORMATION **
IF ( MOD ( STEP, IPRINT ) .EQ. 0 ) THEN
WRITE(*,'(I8,3F10.4)') INT(ACM), RATIO, DRMAX, DOTMIN
ENDIF
C ** WRITE OUT THE CONFIGURATION AT INTERVALS **
IF ( MOD ( STEP, ISAVE ) .EQ. 0 ) THEN
CALL WRITCN ( CNFILE )
CALL CHECK ( SIGMA, DAB, OVRLAP )
IF ( OVRLAP ) STOP 'OVERLAP DURING THE RUN'
ENDIF
100 CONTINUE
C *******************************************************************
C ** ENDS THE LOOP OVER CYCLES **
C *******************************************************************
C ** CHECKS FOR OVRLAPS IN THE FINAL CONFIGURATION **
CALL CHECK ( SIGMA, DAB, OVRLAP )
IF ( OVRLAP ) STOP 'OVERLAP IN FINAL CONFIGURATION'
C ** WRITE OUT THE FINAL CONFIGURATION FROM THE RUN **
CALL WRITCN ( CNFILE )
STOP
END
SUBROUTINE ORIEN ( EXIOLD, EYIOLD, EZIOLD, DOTMIN,
: EXINEW, EYINEW, EZINEW )
C *******************************************************************
C ** FINDS A TRIAL RANDOM ORIENTATION OF A LINEAR MOLECULE. **
C ** **
C ** PRINCIPAL VARIABLES: **
C ** **
C ** REAL EXIOLD,EYIOLD,EZIOLD OLD AXIAL VECTOR FOR I **
C ** REAL EYINEW,EYINEW,EZINEW NEW AXIAL VECTOR FOR I **
C ** REAL DOT DOT PRODUCT OF OLD AND NEW **
C ** AXIAL VECTORS **
C ** REAL DOTMIN MINIMUM ALLOWED DOT PRODUCT **
C ** **
C ** USAGE: **
C ** **
C ** THE METHOD USE A REJECTION TECHNIQUE TO CREATE A TRIAL **
C ** ORIENTATION OF MOLECULE I SUBJECT TO THE CONSTRAINT THAT **
C ** THE COSINE OF THE ANGLE BETWEEN THE OLD AND NEW AXIAL **
C ** VECTORS, DOT, IS GREATER THAN ( 1.0 - DOTMIN ). **
C *******************************************************************
REAL EXIOLD, EYIOLD, EZIOLD, EXINEW, EYINEW, EZINEW, DOTMIN
REAL DOT, XI1, XI2, XI, XISQ
REAL RANF, DUMMY
C *******************************************************************
C ** INITIALISE DOT **
DOT = 0.0
C ** ITERATIVE LOOP **
1000 IF ( ( 1.0 - DOT ) .GE. DOTMIN ) THEN
C ** INITIALISE XISQ **
XISQ = 1.0
C ** INNER ITERATIVE LOOP **
2000 IF ( XISQ .GE. 1.0 ) THEN
XI1 = RANF ( DUMMY ) * 2.0 - 1.0
XI2 = RANF ( DUMMY ) * 2.0 - 1.0
XISQ = XI1 * XI1 + XI2 * XI2
GOTO 2000
ENDIF
XI = SQRT ( 1.0 - XISQ )
EXINEW = 2.0 * XI1 * XI
EYINEW = 2.0 * XI2 * XI
EZINEW = 1.0 - 2.0 * XISQ
DOT = EXINEW * EXIOLD + EYINEW * EYIOLD + EZINEW * EZIOLD
GOTO 1000
ENDIF
RETURN
END
SUBROUTINE TEST ( RXI, RYI, RZI, I, EXI, EYI, EZI, SIGMA,
: DAB, OVRLAP )
COMMON / BLOCK1 / RX, RY,RZ, EX, EY, EZ
C *******************************************************************
C ** CHECKS FOR OVERLAP OF I WITH ALL OTHER MOLECULES. **
C ** **
C ** PRINCIPAL VARIABLES: **
C ** **
C ** INTEGER I THE MOLECULE OF INTEREST **
C ** INTEGER N NUMBER OF MOLECULES **
C ** INTEGER NATOM NUMBER OF ATOMS PER MOLECULE **
C ** REAL RXI,RYI,RZI POSITION OF MOLECULE I **
C ** REAL EXI,EYI,EZI, ORIENTATION OF MOLECULE I **
C ** REAL RX(N),RY(N),RZ(N) MOLECULAR POSITIONS **
C ** REAL EX(N),EY(N),EZ(N) MOLECULAR ORIENTATIONS **
C ** REAL DAB(NATOM) POSITION OF ATOMS IN A MOLECULE **
C ** REAL SIGMA REDUCED ATOM DIAMETER **
C ** LOGICAL OVRLAP TRUE IF MOLECULE I OVERLAPS **
C ** **
C ** USAGE: **
C ** **
C ** CALLED AFTER A TRIAL DISPLACEMENT OF MOLECULE I TO ESTABLISH **
C ** WHETHER THERE IS AN OVERLAP IN THE TRIAL CONFIGURATION. **
C *******************************************************************
INTEGER NATOM, N
PARAMETER ( NATOM = 2, N = 108 )
REAL RX(N), RY(N), RZ(N)
REAL EX(N), EY(N), EZ(N)
REAL RXI, RYI, RZI, EXI, EYI, EZI
REAL SIGMA, DAB(NATOM)
INTEGER I
LOGICAL OVRLAP
REAL RXIJ, RYIJ, RZIJ, EXJ, EYJ, EZJ
REAL RXAB, RYAB, RZAB, DABI, SIGSQ, RABSQ
INTEGER J, IA, JB
C *******************************************************************
OVRLAP = .FALSE.
SIGSQ = SIGMA * SIGMA
C ** LOOPS OVER MOLECULES EXCEPT I **
DO 100 J = 1, N
IF ( J .NE. I ) THEN
EXJ = EX(J)
EYJ = EY(J)
EZJ = EZ(J)
RXIJ = RXI - RX(J)
RYIJ = RYI - RY(J)
RZIJ = RZI - RZ(J)
RXIJ = RXIJ - ANINT ( RXIJ )
RYIJ = RYIJ - ANINT ( RYIJ )
RZIJ = RZIJ - ANINT ( RZIJ )
C ** LOOPS OVER ATOMS **
DO 99 IA = 1, NATOM
DABI = DAB(IA)
DO 98 JB = 1, NATOM
RXAB = RXIJ + EXI * DABI + EXJ * DAB(JB)
RYAB = RYIJ + EYI * DABI + EYJ * DAB(JB)
RZAB = RZIJ + EZI * DABI + EZJ * DAB(JB)
RABSQ = RXAB * RXAB + RYAB * RYAB + RZAB * RZAB
IF ( RABSQ .LT. SIGSQ ) THEN
OVRLAP = .TRUE.
RETURN
ENDIF
98 CONTINUE
99 CONTINUE
ENDIF
100 CONTINUE
RETURN
END
SUBROUTINE CHECK ( SIGMA, DAB, OVRLAP )
COMMON / BLOCK1 / RX, RY, RZ, EX, EY, EZ
C *******************************************************************
C ** ROUTINE TO CHECK FOR OVERLAPS IN A FLUID OF HARD DUMBBELLS **
C ** **
C ** PRINCIPAL VARIABLES: **
C ** **
C ** INTEGER N NUMBER OF MOLECULES **
C ** INTEGER NATOM NUMBER OF ATOMS PER MOLECULE **
C ** REAL RX(N),RY(N),RZ(N) MOLECULAR POSITIONS **
C ** REAL EX(N),EY(N),EZ(N) MOLECULAR ORIENTATIONS **
C ** REAL DAB(NATOM) POSITION OF ATOMS IN A MOLECULE **
C ** REAL SIGMA REDUCED ATOM DIAMETER **
C ** LOGICAL OVRLAP TRUE IF TWO DUMBELLS OVERLAP **
C ** **
C ** USAGE: **
C ** **
C ** CALLED AT INTERVALS DURING THE RUN TO CHECK FOR OVERLAPS. IF **
C ** OVRLAP IS RETURNED WITH A TRUE VALUE THEN THERE IS AN ERROR **
C ** IN THE PROGRAM AND THE EXECUTION IS STOPPED. **
C *******************************************************************
INTEGER NATOM, N
PARAMETER ( NATOM = 2, N = 108 )
REAL RX(N), RY(N), RZ(N)
REAL EX(N), EY(N), EZ(N)
REAL SIGMA, DAB(NATOM)
LOGICAL OVRLAP
REAL RXI, RYI, RZI, RXIJ, RYIJ, RZIJ, EXI, EYI, EZI
REAL EXJ, EYJ, EZJ, RXAB, RYAB, RZAB, DABI, SIGSQ, RABSQ
INTEGER I, J, IA, JB
C *******************************************************************
OVRLAP = .FALSE.
SIGSQ = SIGMA * SIGMA
C ** LOOPS OVER MOLECULES **
DO 100 I = 1, N - 1
RXI = RX(I)
RYI = RY(I)
RZI = RZ(I)
EXI = EX(I)
EYI = EY(I)
EZI = EZ(I)
DO 99 J = I + 1, N
RXIJ = RXI - RX(J)
RYIJ = RYI - RY(J)
RZIJ = RZI - RZ(J)
RXIJ = RXIJ - ANINT ( RXIJ )
RYIJ = RYIJ - ANINT ( RYIJ )
RZIJ = RZIJ - ANINT ( RZIJ )
EXJ = EX(J)
EYJ = EY(J)
EZJ = EZ(J)
C ** LOOPS OVER ATOMS **
DO 98 IA = 1, NATOM
DABI = DAB(IA)
DO 97 JB = 1, NATOM
RXAB = RXIJ + EXI * DABI + EXJ * DAB(JB)
RYAB = RYIJ + EYI * DABI + EYJ * DAB(JB)
RZAB = RZIJ + EZI * DABI + EZJ * DAB(JB)
RABSQ = RXAB * RXAB + RYAB * RYAB + RZAB * RZAB
IF ( RABSQ .LT. SIGSQ ) THEN
OVRLAP = .TRUE.
RETURN
ENDIF
97 CONTINUE
98 CONTINUE
99 CONTINUE
100 CONTINUE
RETURN
END
SUBROUTINE READCN ( CNFILE )
COMMON / BLOCK1 / RX, RY, RZ, EX, EY, EZ
C *******************************************************************
C ** SUBROUTINE TO READ IN THE CONFIGURATION FROM UNIT 10 **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
CHARACTER CNFILE*(*)
REAL RX(N), RY(N), RZ(N), EX(N), EY(N), EZ(N)
INTEGER CNUNIT
PARAMETER ( CNUNIT = 10 )
INTEGER NN
C ********************************************************************
OPEN ( UNIT = CNUNIT, FILE = CNFILE, STATUS = 'OLD',
: FORM = 'UNFORMATTED' )
READ ( CNUNIT ) NN
IF ( NN .NE. N ) STOP 'N ERROR IN READCN'
READ ( CNUNIT ) RX, RY, RZ
READ ( CNUNIT ) EX, EY, EZ
CLOSE ( UNIT = CNUNIT )
RETURN
END
SUBROUTINE WRITCN ( CNFILE )
COMMON / BLOCK1 / RX, RY, RZ, EX, EY, EZ
C *******************************************************************
C ** SUBROUTINE TO WRITE OUT THE CONFIGURATION TO UNIT 10 **
C *******************************************************************
INTEGER N
PARAMETER ( N = 108 )
CHARACTER CNFILE*(*)
REAL RX(N), RY(N), RZ(N), EX(N), EY(N), EZ(N)
INTEGER CNUNIT
PARAMETER ( CNUNIT = 10 )
C ********************************************************************
OPEN ( UNIT = CNUNIT, FILE = CNFILE, STATUS = 'UNKNOWN',
: FORM = 'UNFORMATTED' )
WRITE ( CNUNIT ) N
WRITE ( CNUNIT ) RX, RY, RZ
WRITE ( CNUNIT ) EX, EY, EZ
CLOSE ( UNIT = CNUNIT )
RETURN
END
REAL FUNCTION RANF ( DUMMY )
C *******************************************************************
C ** RETURNS A UNIFORM RANDOM VARIATE IN THE RANGE 0 TO 1. **
C ** **
C ** *************** **
C ** ** WARNING ** **
C ** *************** **
C ** **
C ** GOOD RANDOM NUMBER GENERATORS ARE MACHINE SPECIFIC. **
C ** PLEASE USE THE ONE RECOMMENDED FOR YOUR MACHINE. **
C *******************************************************************
INTEGER L, C, M
PARAMETER ( L = 1029, C = 221591, M = 1048576 )
INTEGER SEED
REAL DUMMY
SAVE SEED
DATA SEED / 0 /
C *******************************************************************
SEED = MOD ( SEED * L + C, M )
RANF = REAL ( SEED ) / M
RETURN
END