# L-J Potential-Distance of equilibrium

1. May 31, 2013

### Pahoo

LJ-Potential

1. The problem statement, all variables and given/known data
Find distance of equilibrium for:
1.
Uvdw(r)=-A/r6+B/r12
A=10-77 Jm6
B=10-134 Jm12

2. Relevant equations

Uvdw(r)=-A/r6+B/r12

3. The attempt at a solution
It is suppose that r is the distance, but I have not any idea how to calculate this.

2. May 31, 2013

### Staff: Mentor

This isn't really an engineering question, though. Would you like me to move this to the HH/Advanced Physics forum?

3. May 31, 2013

### Pahoo

1. The problem statement, all variables and given/known data
Find distance of equilibrium for:
1.
Uvdw(r)=-A/r6+B/r12
A=10-77 Jm6
B=10-134 Jm12

2. Relevant equations

Uvdw(r)=-A/r6+B/r12

3. The attempt at a solution
It is suppose that r is the distance, I suppose that r=(2A/B)(1/6)
and 0=2A-Br6.
However I`m totally lost

Last edited: May 31, 2013
4. May 31, 2013

### Pahoo

Thanks

5. May 31, 2013

### Staff: Mentor

The equilibrium distance is the minimum of the potential. How do you find a minimum?

6. Jun 3, 2013

### Pahoo

ok, finally I figure out how to calculate the minimun which is r = (2^(1/6) B^(1/6))/A^(1/6). Am I right?

7. Jun 3, 2013

### Staff: Mentor

Looks good. I would express it as $\displaystyle \left(\frac{2B}{A}\right)^{\frac{1}{6}}$