VNIITF EAM¶

Description¶

The vniitf_force operator computes the analytic EAM potential developed at VNIITF (single species). With \(x = r/r_{t0} - 1\) and \(S(r)\) a smoothing function that goes from 1 at \(r_{\min}\) to 0 at \(r_{\max}\):

\[ \phi(r) = \left[E_0 - \frac{2E_{coh}}{Z}\left(1 + \alpha x + \eta x^2 + \left(\mu + \frac{\alpha^3 D\,r_{t0}}{r}\right)x^3\right)e^{-\alpha x}\right] S(r) \]

\[ \rho(r) = \frac{e^{-\beta x}}{Z}\,S(r), \qquad F(\rho) = A\,E_{coh}\,\rho^{n}\left(\ln \rho^{n} - 1\right) \]

The smoothing function is, with \(u = \dfrac{r_{\max} - r}{r_{\max} - r_{\min}}\) clamped to \([0,1]\),

\[ S(r) = u^4\left(35 - 84u + 70u^2 - 20u^3\right) \]

See the EAM overview for the total energy and the available operators (vniitf_force, vniitf_emb, vniitf_force_reuse_emb, vniitf_init).

Parameter	Units	Description
`rmax`	distance	Distance where the smoothing function reaches 0
`rmin`	distance	Distance where the smoothing function starts
`rt0`	distance	Characteristic radius \(r_{t0}\)
`Ecoh`	energy	Cohesive energy \(E_{coh}\)
`E0`	energy	Constant energy term \(E_0\) of the pair interaction
`beta`	—	Decay rate \(\beta\) of the electron density
`A`	—	Embedding amplitude \(A\)
`Z`	—	Number of neighbors in the reference structure
`n`	—	Embedding exponent \(n\)
`alpha`, `D`, `eta`, `mu`	—	Pair term coefficients

YAML syntax¶

vniitf_force:
  rcut: VALUE UNITS
  parameters:
    rmax: VALUE UNITS
    rmin: VALUE UNITS
    rt0: VALUE UNITS
    Ecoh: VALUE UNITS
    E0: VALUE UNITS
    beta: VALUE
    A: VALUE
    Z: VALUE
    n: VALUE
    alpha: VALUE
    D: VALUE
    eta: VALUE
    mu: VALUE

VALUE = Physical value of the intended parameter.
UNITS = Units of the provided value that will be passed to the conversion helper for internal units conversion.

Usage example¶

Tin

vniitf_force:
  rcut: 5.599 ang
  parameters:
    rmax: 5.599 ang
    rmin: 1.0 ang
    rt0: 3.437 ang
    Ecoh: 2.956031e-19 J
    E0: 5.15003855e-20 J
    beta: 6.000E+00
    A: 1.401E+00
    Z: 7.618E+00
    n: 0.724E+00
    alpha: 3.072E+00
    D: 1.450E-01
    eta: 2.720E+00
    mu: -1.87E+00

compute_force: vniitf_force

The complete input is exaStamp/data/regression_new/potentials/eam/eam_vniitf/single_specy.msp.