### Coulomb and Modified Van der Waals interations

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Coulomb and Van der Waals interations (Vm=0):
Uij(r)=4 f e2aij-1 [(aij/r)12 - (aij/r)6] + e2qiqj/r
aij=ri+rj, f=0.004

Modified Coulomb and Van der Waals interations (Vm=1):
Uij(r)=4 f e2(2aij)-1 {[2aij/(r+aij)]12 - Vv[2aij/(r+aij)]6} + e2qiqj/(r+aij)
aij=ri+rj, f=0.004

In the simulation, the velocity of a particle is proportional to the force that act on the particle. The particles will settle into a configuration which locally minimize the total energy.
• Uij: The interaction potential between the i-th and j-th particles.
• qi, qj: The charges of the i-th and j-th particles.
• ri, rj: The radius of the i-th and j-th particles.
• Vm: Vm=0 for standard Coulomb and Van der Waals interaction. Vm=1 for modified Coulomb and Van der Waals interaction.
• Vv: Vv=1 for standard Van der Waals interaction. Vv=0 turns off the attractive part of Van der Waals interaction.

### Usage

• Restart: Restart simulation with a random particle configuration.
• +/-N1,+/-N2: Increase/decrease N1 or N2, the number of the red or blue particles.*
• +/-q1,+/-q2: Increase/decrease q1 or q2, the charges of the red or blue particles.*
• +/-r1,+/-r2: Increase/decrease r1 or r2, the radii of the red or blue particles
• +/-T: Increase/decrease temperature
• Vv: toggles between Vv=1 and Vv=0
• Vm: toggles between Vm=1 and Vm=0.*
• In/Out: Zoom in/out
• +/-Sp: Increase/decrease simulation speed. The simulation becomes unstable when Sp is too large. In this case, descrease Sp.
* The speed Sp is set to zero after clicking the button. Increase Sp to start the run.

### Experiments

• Click Restart many times (like ~ 20) to see if a nice crystal or other nice configurations can form.
• Change Vm=0 to get the standard Van der Waals interaction. Now click Restart many times to see if a nice crystal or other nice configurations can form.
• Change the charges to q1=5 and q2=-5. Now click Restart to see if a nice crystal or other nice configurations can form.
• Increase temerature T to 1000, and then decrease T slowly back to 0.
• Experiment with different q1/q2, N1/N2, r1/r2. Try to start with a few particles and then add particles one by one.