Volume-change Trial Move5. Examination of Java Code

public void thisTrial(Phase phase) {

double hOld, hNew, vOld, vNew;

vOld = phase.volume();

hOld = phase.potentialEnergy.currentValue() //current value of the enthalpy

+ pressure*vOld*Constants.PV2T; //PV2T is a conversion factor

double vScale = (2.*rand.nextDouble()-1.)*stepSize; //choose step size

vNew = vOld * Math.exp(vScale); //Step in ln(V)

double rScale = Math.exp(vScale/(double)Simulation.D); //evaluate linear scaling

phase.inflate(rScale); //scale all center-of-mass coordinates

hNew = phase.potentialEnergy.currentValue() //new value of the enthalpy

+ pressure*vNew*Constants.PV2T;

if(hNew >= Double.MAX_VALUE || //decide acceptance

Math.exp(-(hNew-hOld)/parentIntegrator.temperature+(phase.moleculeCount+1)*vScale)

< rand.nextDouble())

{ //reject; put coordinates back to original positions

phase.inflate(1.0/rScale);

}

nAccept++; //accept

}

Have a look at a simple NPT MC simulation applet

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