C ******************************************************************* C ** THIS FORTRAN CODE IS INTENDED TO ILLUSTRATE POINTS MADE IN ** C ** THE TEXT. TO OUR KNOWLEDGE IT WORKS CORRECTLY. HOWEVER IT IS ** C ** THE RESPONSIBILITY OF THE USER TO TEST IT, IF IT IS USED IN A ** C ** RESEARCH APPLICATION. ** C ******************************************************************* C ******************************************************************* C ** FICHE F.25 ** C ** CALCULATION OF TRANSLATIONAL ORDER PARAMETER (MELTING FACTOR).** C ******************************************************************* SUBROUTINE ORDER ( KLATX, KLATY, KLATZ, PARAM ) COMMON / BLOCK1 / RX, RY, RZ, VX, VY, VZ, FX, FY, FZ C ******************************************************************* C ** CALCULATION OF TRANSLATIONAL ORDER PARAMETER (MELTING FACTOR).** C ** ** C ** CLASSICALLY, THE ORDER PARAMETER IS A NORMALIZED SUM OF ** C ** COSINE TERMS WHICH SHOULD BE UNITY IN THE PERFECT LATTICE ** C ** AND FLUCTUATE AROUND ZERO FOR A DISORDERED SYSTEM. ** C ** HOWEVER, THIS IS NOT ORIGIN-INDEPENDENT: WITH AN UNSUITABLE ** C ** CHOICE OF ORIGIN IT COULD VANISH EVEN IN A PERFECT LATTICE. ** C ** ACCORDINGLY, WE CALCULATE HERE A QUANTITY THAT IS INDEPENDENT ** C ** OF THE ORIGIN OF COORDINATES. ** C ** IT SHOULD BE UNITY IN A LATTICE FOR WHICH A RECIPROCAL VECTOR ** C ** (KLATX,KLATY,KLATZ) IS SUPPLIED. ** C ** IT SHOULD BE POSITIVE BUT SMALL, OF ORDER SQRT(N) IN A ** C ** DISORDERED SYSTEM. ** C ** ** C ** PRINCIPAL VARIABLES: ** C ** ** C ** INTEGER N NUMBER OF MOLECULES ** C ** REAL RX(N),RY(N),RZ(N) MOLECULAR COORDINATES ** C ** REAL VX(N),VY(N),VZ(N) MOLECULAR VELOCITIES (NOT USED) ** C ** REAL FX(N),FY(N),FZ(N) MOLECULAR FORCES (NOT USED) ** C ** REAL KLATX,KLATY,KLATZ RECIPROC. VECTOR OF INITIAL LATTICE ** C ** REAL PARAM RESULT: ORDER PARAMETER ** C ******************************************************************* INTEGER N PARAMETER ( N = 108 ) REAL KLATX, KLATY, KLATZ, PARAM REAL RX(N), RY(N), RZ(N) REAL VX(N), VY(N), VZ(N) REAL FX(N), FY(N), FZ(N) INTEGER I REAL SINSUM, COSSUM C ******************************************************************* SINSUM = 0.0 COSSUM = 0.0 DO 100 I = 1, N COSSUM = COSSUM + COS ( KLATX * RX(I) : + KLATY * RY(I) : + KLATZ * RZ(I) ) SINSUM = SINSUM + SIN ( KLATX * RX(I) : + KLATY * RY(I) : + KLATZ * RZ(I) ) 100 CONTINUE COSSUM = COSSUM / REAL ( N ) SINSUM = SINSUM / REAL ( N ) PARAM = SQRT ( COSSUM ** 2 + SINSUM ** 2 ) RETURN END