## Two Dimensional System of the LJ Model

If you would like to work on your LJ Model only on two dimensions, you will need to modify this part of the program. Also your input file should be modified. See demonstration below:

### Before:

```Molec_dyn.f
DO  I = 1,NATOM
END DO

DO I = 1,NATOM
KE = KE + (U(I)**2 + V(I)**2 + W(I)**2)/2
END DO
WRITE(3,99) K*0.0, 0, PE, KE, PE+KE
DO I = 1,NATOM
WRITE(3,99) K*H, I, X(I), Y(I), Z(I)
WRITE(3,99) K*H, I, U(I), V(I), W(I)
END DO

* Main loop
DO K = 1, NSTEP
DO I = 1,NATOM
X(I) = X(I) + H*(U(I) + HO2*FX(I,B1))
Y(I) = Y(I) + H*(V(I) + HO2*FY(I,B1))
Z(I) = Z(I) + H*(W(I) + HO2*FZ(I,B1))
END DO
CALL FORCE_LJ(NATOM,NATOMX,X,Y,Z,B2,FX,FY,FZ)
DO I = 1,NATOM
U(I) = U(I) + HO2*(FX(I,B1) + FX(I,B2))
V(I) = V(I) + HO2*(FY(I,B1) + FY(I,B2))
W(I) = W(I) + HO2*(FZ(I,B1) + FZ(I,B2))
END DO

Potentional_lj.f
IF (MOD(K,PRNFREQ) .EQ. 0) THEN
PE = POTENTIAL_LJ(NATOM,X,Y,Z)
KE = 0
DO I = 1,NATOM
KE = KE + (U(I)**2 + V(I)**2 + W(I)**2)/2
END DO
WRITE(3,99)INT(1000.*K*H),0,PE,KE,PE+KE
DO I = 1,NATOM
WRITE(3,99)K*H,I,X(I),Y(I),Z(I)
WRITE(3,99)K*H,I,U(I),V(I),W(I)
END DO
END IF

* Compute potential.
DO I = 1, NATOM-1
DO J = I+1, NATOM
RIJSQ = 1.0/((X(I)-X(J))**2 + (Y(I)-Y(J))**2 +
\$           (Z(I)-Z(J))**2)
RIJM6 = RIJSQ*RIJSQ*RIJSQ
POT = POT + RIJM6*(RIJM6 - 2.0)
END DO
END DO
```

### After:

```Molec_dyn.f
DO  I = 1,NATOM
END DO

DO I = 1,NATOM
KE = KE + (U(I)**2 + V(I)**2)/2
END DO
WRITE(3,99) K*0.0, 0, PE, KE, PE+KE
DO I = 1,NATOM
WRITE(3,99) K*H, I, X(I), Y(I)
WRITE(3,99) K*H, I, U(I), V(I)
END DO

* Main loop
DO K = 1, NSTEP
DO I = 1,NATOM
X(I) = X(I) + H*(U(I) + HO2*FX(I,B1))
Y(I) = Y(I) + H*(V(I) + HO2*FY(I,B1))
END DO
CALL FORCE_LJ(NATOM,NATOMX,X,Y,Z,B2,FX,FY,FZ)
DO I = 1,NATOM
U(I) = U(I) + HO2*(FX(I,B1) + FX(I,B2))
V(I) = V(I) + HO2*(FY(I,B1) + FY(I,B2))
END DO

Potentional_lj.f
IF (MOD(K,PRNFREQ) .EQ. 0) THEN
PE = POTENTIAL_LJ(NATOM,X,Y,Z)
KE = 0
DO I = 1,NATOM
KE = KE + (U(I)**2 + V(I)**2)/2
END DO
WRITE(3,99)INT(1000.*K*H),0,PE,KE,PE+KE
DO I = 1,NATOM
WRITE(3,99)K*H,I,X(I),Y(I)
WRITE(3,99)K*H,I,U(I),V(I)
END DO
END IF

* Compute potential.
DO I = 1, NATOM-1
DO J = I+1, NATOM
RIJSQ = 1.0/((X(I)-X(J))**2 + (Y(I)-Y(J))**2
RIJM6 = RIJSQ*RIJSQ*RIJSQ
POT = POT + RIJM6*(RIJM6 - 2.0)
END DO
END DO
```