# General2Potential¶

class General2Potential(particleType1, particleType2, A, C, rho, r_i=None, r_cut=None)

Constructor of the potential.

Parameters: particleType1 (ParticleType or ParticleIdentifier) – Identifier of the first particle type. particleType2 (ParticleType or ParticleIdentifier) – Identifier of the second particle type. A (PhysicalQuantity of type length**2 * energy) – Potential parameter. C (PhysicalQuantity of type length * energy) – Potential parameter. rho (PhysicalQuantity of type length) – Potential parameter. r_i (PhysicalQuantity of type length) – The inner cutoff radius where the smoothing of the potential starts. r_i must be smaller than r_cut. r_cut (PhysicalQuantity of type length) – The cutoff radius of this potential.
getAllParameterNames()

Return the names of all used parameters as a list.

getAllParameters()

Return all parameters of this potential and their current values as a <parameterName / parameterValue> dictionary.

static getDefaults()

Get the default parameters of this potential and return them in form of a dictionary of <parameter name, default value> key-value pairs.

getParameter(parameterName)

Get the current value of the parameter parameterName.

setA(A)

Set the parameter A.

Parameters: A (PhysicalQuantity of type length**2 * energy) – Potential parameter.
setC(C)

Set the parameter C.

Parameters: C (PhysicalQuantity of type length * energy) – Potential parameter.
setCutoff(r_cut)

Set the cutoff radius for this potential.

Parameters: r_cut (PhysicalQuantity of type length) – The cutoff radius of this potential.
setInnerCutoff(r_i)

Set the inner cutoff radius for this potential.

Parameters: r_i (PhysicalQuantity of type length) – The inner cutoff radius (distance where the spline-smoothing starts).
setParameter(parameterName, value)

Set the parameter parameterName to the given value.

Parameters: parameterName (str) – The name of the parameter that will be modified. value – The new value that will be assigned to the parameter parameterName.
setRho(rho)

Set the parameter rho.

Parameters: rho (PhysicalQuantity of type length) – Potential parameter.

## Notes¶

The General2Potential defines a pair potential of the form

$V_{ij}(r) = \frac{A}{r^2} e^{-r/\rho} - \frac{C}{r} \, .$

At long distances this potential is brought smoothly to zero between the inner cutoff r_i and the outer cutoff r_cut, using a 5th order spline function. This ensures that there are no discontinuites in the forces as atoms are brought closer together, and that the energy is properly conserved. The applied potential $$U(r)$$ is given as:

$U(r) = V_{ij}(r) \times S(r)$

where $$V_{ij}(r)$$ is the pair potential and $$S(r)$$ is the spline function. The values of the spline function are:

• 1 when $$r \le r_i$$
• In the range $$[0,1]$$ when $$r_i < r < r_{cut}$$
• 0 when $$r \ge r_{cut}$$