MEAM + Lennard-Jones¶

Description¶

The meam_lj_force operator mixes a MEAM potential for one species with Lennard-Jones interactions for the other species pairs. A typical use is a metal (described by MEAM) in contact with a gas or a fluid (described by Lennard-Jones).

Pairs of atoms of the species meam_type interact through MEAM. MEAM only "sees" atoms of this species.
The other species pairs listed in lj_parameters interact through a Lennard-Jones potential, shifted to zero at its cutoff:

\[ E_{\mathrm{LJ}}(r) = 4\varepsilon\left[\left(\frac{\sigma}{r}\right)^{12} - \left(\frac{\sigma}{r}\right)^{6}\right] - E_{\mathrm{LJ}}^{\mathrm{raw}}(r_{\mathrm{cut}}) \quad \text{for} \quad r < r_{\mathrm{cut}} \]

Species pairs that are not listed do not interact.

At most XSTAMP_MEAM_MULTIMAT_MAX_TYPES species (4 by default, see the MEAM overview) can be used.

Syntax

meam_lj_force:
  rcut: <float>
  ghost: <bool>
  meam_type: <string>
  parameters: { <MEAM parameters> }
  lj_parameters:
    - { type_a: <string>, type_b: <string>, rcut: <float>, epsilon: <float>, sigma: <float> }

Parameters

rcut:           float, required       # Base cutoff radius of the MEAM part.
ghost:          bool, default true    # true: compute the MEAM terms on ghost atoms too (ghost layer of 2 x cutoff, no extra communication). false: ghost layer of 1 x cutoff, ghost forces must be sent back (include config_update_symmetric_forces.msp).
meam_type:      string, required      # Species described by MEAM.
parameters:     map, required         # MEAM parameters, see the MEAM page.
lj_parameters:  list, required        # Lennard-Jones parameters for the other species pairs.

Usage example¶

Tin in an O2/N2 atmosphere

includes: [ config_update_symmetric_forces.msp ]   # needed with ghost: false

grid_flavor: grid_flavor_multimat

meam_lj_force:
  ghost: false
  meam_type: Sn
  rcut: 4.17 ang
  parameters:
    rmax: 4.17 ang
    rmin: 0.0
    Ecoh: 4.93474273599999995322e-19 J
    E0: 4.93474273599999995322e-19 J
    A: 1.000E+00
    r0: 3.44 ang
    alpha: 6.200E+00
    delta: 0.000E+00
    beta0: 6.200E+00
    beta1: 6.000E+00
    beta2: 6.000E+00
    beta3: 6.000E+00
    t0: 1.000E+00
    t1: 4.500E+00
    t2: 6.500E+00
    t3: -0.183E+00
    s0: 1.440E+02
    s1: 0.000E+00
    s2: 0.000E+00
    s3: 0.000E+00
    Cmin: 0.800E+00
    Cmax: 2.800E+00
    Z: 1.200E+01
    rc: 4.0 ang
    rp: 0.1 ang
  lj_parameters:
    - { type_a: O2 , type_b: O2 , rcut: 8 ang , epsilon: 162.2273150e-23 J , sigma: 3.58 ang }
    - { type_a: N2 , type_b: N2 , rcut: 8 ang , epsilon: 131.3005758e-23 J , sigma: 3.70 ang }
    - { type_a: O2 , type_b: N2 , rcut: 8 ang , epsilon: 145.9470447e-23 J , sigma: 3.64 ang }
    - { type_a: O2 , type_b: Sn , rcut: 8 ang , epsilon: 150.0000000e-24 J , sigma: 3.00 ang }
    - { type_a: N2 , type_b: Sn , rcut: 8 ang , epsilon: 150.0000000e-24 J , sigma: 3.00 ang }

compute_force: meam_lj_force

Complete inputs are in exaStamp/data/regression_new/potentials/meam_lj/ (Sn_O2_N2.msp).