ZBL¶

class hoomd.md.pair.ZBL(nlist, default_r_cut=None, default_r_on=0.0)¶

Bases: Pair

ZBL pair force.

Parameters:

nlist (hoomd.md.nlist.NeighborList) – Neighbor list.
default_r_cut (float) – Default cutoff radius \([\mathrm{length}]\).
default_r_on (float) – Default turn-on radius \([\mathrm{length}]\).

ZBL computes the Ziegler-Biersack-Littmark pair force on every particle in the simulation state:

\[\begin{split}U(r) = \frac{Z_i Z_j e^2}{4 \pi \epsilon_0 r_{ij}} \left[ 0.1818 \exp \left( -3.2 \frac{r_{ij}}{a_F} \right) \right. \\ + 0.5099 \exp \left( -0.9423 \frac{r_{ij}}{a_F} \right) \\ + 0.2802 \exp \left( -0.4029 \frac{r_{ij}}{a_F} \right) \\ + \left. 0.02817 \exp \left( -0.2016 \frac{r_{ij}}{a_F} \right) \right]\end{split}\]

Where each parameter is defined as:

\(Z_i\) - Z_i - Atomic number of species i \([\mathrm{dimensionless}]\)
\(Z_j\) - Z_j - Atomic number of species j \([\mathrm{dimensionless}]\)
\(e\) - elementary_charge - The elementary charge \([\mathrm{charge}]\)
\(a_F = \frac{0.8853 a_0}{ Z_i^{0.23} + Z_j^{0.23} }\), where \(a_0\) is the Bohr radius \([\mathrm{length}]\)

Example:

nl = nlist.Cell()
zbl = pair.ZBL(default_r_cut=3.0, nlist=nl)

Zi = 54
Zj = 7
e = 1
a0 = 1
aF = 0.8853 * a0 / (Zi**(0.23) + Zj**(0.23))

zbl.params[('A', 'B')] = dict(qi=Zi*e, qj=Zj*e, aF=aF)

Members inherited from AutotunedObject:

property kernel_parameters¶: Kernel parameters. Read more...

property is_tuning_complete¶: Check if kernel parameter tuning is complete. Read more...

tune_kernel_parameters()¶: Start tuning kernel parameters. Read more...

Members inherited from Force:

additional_energy¶: Additional energy term. Read more...

additional_virial¶: Additional virial tensor term \(W_\mathrm{additional}\). Read more...

cpu_local_force_arrays¶: Local force arrays on the CPU. Read more...

energies¶: Energy contribution \(U_i\) from each particle. Read more...

energy¶: The potential energy \(U\) of the system from this force. Read more...

forces¶: The force \(\vec{F}_i\) applied to each particle. Read more...

gpu_local_force_arrays¶: Local force arrays on the GPU. Read more...

torques¶: The torque \(\vec{\tau}_i\) applied to each particle. Read more...

virials¶: Virial tensor contribution \(W_i\) from each particle. Read more...

Members inherited from Pair:

nlist¶: Neighbor list used to compute the pair force. Read more...

mode¶: Energy smoothing/cutoff mode. Read more...

r_cut¶: Cuttoff radius beyond which the energy and force are 0. Read more...

r_on¶: Radius at which the XPLOR smoothing function starts. Read more...

compute_energy()¶: Compute the energy between two sets of particles. Read more...

Members defined in ZBL:

params¶

The ZBL potential parameters. The dictionary has the following keys:

q_i (float, required) - \(q_i=Z_i \frac{e}{\sqrt{4 \pi \epsilon_0}}\) \([\mathrm{charge}]\)
q_j (float, required) - \(q_j=Z_j \frac{e}{\sqrt{4 \pi \epsilon_0}}\) \([\mathrm{charge}]\)
a_F (float, required) - \(a_F = \frac{0.8853 a_0}{ Z_i^{0.23} + Z_j^{0.23} }\) \([\mathrm{length}]\)

Type: TypeParameter [tuple [particle_type, particle_type], dict]