pair_style smatb command

Accelerator Variants: smatb/omp

pair_style smatb/single command

Accelerator Variants: smatb/single/omp

Syntax

pair_style style args

style = smatb or smatb/single
args = none

Examples

pair_style smatb
pair_coeff 1 1 2.88 10.35 4.178 0.210 1.818 4.07293506 4.9883063257983666

pair_style smatb/single
pair_coeff 1 1 2.88 10.35 4.178 0.210 1.818 4.07293506 4.9883063257983666

Description

Added in version 4May2022.

The smatb and smatb/single styles compute the Second Moment Approximation to the Tight Binding (Cyrot), (Gupta2), (Rosato), given by

\[E_{i} = \sum_{j,R_{ij}\leq R_{c}} \alpha(R_{ij}) - \sqrt{\sum_{j,R_{ij}\leq R_{c}}\Xi^2(R_{ij})}\]

\(R_{ij}\) is the distance between the atom \(i\) and \(j\). And the two functions \(\alpha\left(r\right)\) and \(\Xi\left(r\right)\) are:

\[\begin{split}\alpha\left(r\right)=\left\lbrace\begin{array}{ll} A e^{-p \left(\frac{r}{R_{0}}-1\right)} & r < R_{sc}\\ a_3\left(r-R_{c}\right)^3+a_4\left(r-R_{c}\right)^4 +a_5\left(r-R_{c}\right)^5& R_{sc} < r < R_{c} \end{array} \right.\end{split}\]

\[\begin{split}\Xi\left(r\right)=\left\lbrace\begin{array}{ll} \xi e^{-q \left(\frac{r}{R_{0}}-1\right)} & r < R_{sc}\\ x_3\left(r-R_{c}\right)^3+x_4\left(r-R_{c}\right)^4 +x_5\left(r-R_{c}\right)^5& R_{sc} < r < R_{c} \end{array} \right.\end{split}\]

The polynomial coefficients \(a_3\), \(a_4\), \(a_5\), \(x_3\), \(x_4\), \(x_5\) are computed by LAMMPS: the two exponential terms and their first and second derivatives are smoothly reduced to zero, from the inner cutoff \(R_{sc}\) to the outer cutoff \(R_{c}\).

The smatb/single style is an optimization when using only a single atom type.

Coefficients

The following coefficients must be defined for each pair of atom types via the pair_coeff command as in the examples above, or in the data file or restart files read by the read_data or read_restart commands, or by mixing as described below:

\(R_{0}\) (distance units)
\(p\) (dimensionless)
\(q\) (dimensionless)
\(A\) (energy units)
\(\xi\) (energy units)
\(R_{cs}\) (distance units)
\(R_{c}\) (distance units)

Note that: \(R_{0}\) is the nearest neighbor distance, usually coincides with the diameter of the atoms

See the run_style command for details.

Styles with a gpu, intel, kk, omp, or opt suffix are functionally the same as the corresponding style without the suffix. They have been optimized to run faster, depending on your available hardware, as discussed on the Accelerator packages page. The accelerated styles take the same arguments and should produce the same results, except for round-off and precision issues.

These accelerated styles are part of the GPU, INTEL, KOKKOS, OPENMP, and OPT packages, respectively. They are only enabled if LAMMPS was built with those packages. See the Build package page for more info.

You can specify the accelerated styles explicitly in your input script by including their suffix, or you can use the -suffix command-line switch when you invoke LAMMPS, or you can use the suffix command in your input script.

See the Accelerator packages page for more instructions on how to use the accelerated styles effectively.

Mixing info

For atom type pairs I,J and I != J the coefficients are not automatically mixed.

Restrictions

These pair styles are part of the SMTBQ package and are only enabled if LAMMPS is built with that package. See the Build package page for more info.

These pair styles require the newton setting to be “on” for pair interactions.

Default

none

(Cyrot) Cyrot-Lackmann and Ducastelle, Phys Rev. B, 4, 2406-2412 (1971).

(Gupta2) Gupta ,Phys Rev. B, 23, 6265-6270 (1981).

(Rosato) Rosato and Guillope and Legrand, Philosophical Magazine A, 59.2, 321-336 (1989).