Sandia National Laboratories Tramonto

Interaction Potential Control Parameters

These switches control the type of wall-fluid and wall-wall interaction potential models that are to be used in the calculation.

  • Ipot_wf_n[Nwall_type](int array): An array to select the type of neutral interactions between the fluid particles and the surfaces. Each surface type must have an entry. Options are:
    • 0: VEXT_NONE: No interaction.
    • 1: VEXT_HARD: An infinitely hard wall. Vext=VEXT_MAX inside the surface geometry plus a shell of width 1/2 Sigma_wf.
    • 2: VEXT_1D: A 1-dimensional (1D) potential used in a 1D calculation. The specific functional form is set by Type_vext1D(see below).
    • 3: VEXT_1D_XMIN: A 1D potential to be used in a 2D or 3D calculation. The algorithm finds the minimum distance from each surface and uses those distances to compute the external field. The 1D potential function is set with Type_vext1D.
    • 4: VEXT_1D_ORIENTATION: A 1D potential used in a 2D or 3D calculation. The algorithm finds the distance to the nearest surfaces in the Orientation direction. Those distances, x are used to compute the external field. The 1D potential function is selected with Type_vext1D.
    • 5: VEXT_3D_INTEGRATED: Start with a 3D atomistic potential (defined by the parameter Type_vext3D), and numerically integrate that potential over the surface of interest from every point in the fluid domain. This allows an arbitrary surface geometry to be composed of say Lennard-Jones atoms at a certain density without representing them explicitly.
    • 6: VEXT_ATOMIC: Surfaces are atoms, and a 3D interaction potential (defined by Type_vext3D) is used directly to calculate the external field.
  • Lhard_surfaces(int): Logical (0=FALSE, 1=TRUE) that controls the application of integration stencils at the boundaries. If TRUE, a step function at the boundary is resolved carefully based on local elements that surround the boundary node. This can be FALSE for all soft potentials. It should be TRUE to obtain accurate density sum rules at hard surfaces.
  • Type_vext1D(int): Select form for 1D potentials in the problem. Note that at the time of the v2.1 release this parameter is not dependent on the surface type, and all 1D potentials must have the same functional form. See the file dft_vext1D.c for parameters associated with a specific case.
    • 0: LJ9_3_CS: The cut and shifted Lennard-Jones 9-3 wall for 1D systems of infinite planar walls.
    • 1: LJ9_3_v2_CS: Same functional form as LJ9_3_CS, but with different prefactors.
    • 2: LJ9_3_noCS: The 9-3 Lennard-Jones potential without the cut and shift.
    • 3: LJ9_3_shiftX_CS: This option shifts the usual 9-3 LJ wall potential by a factor Delta_ff=(Sigma_ff-1)/2.
    • 4: REPULSIVE9_noCS: This is a purely repulsive wall. No cut and shift.
    • 5: EXP_ATT_noCS: An external field based on a decaying exponential. No cut and shift.
  • Type_vext3D(int): Select form for 3D external field potentials in the problem. Note that at the time of the v2.1 release this parameter is not dependent on the surface type, and all 3D potentials must have the same functional form. Choices are identical to Type_pairPot; however, the interaction potential parameters here are all based on wall-fluid parameters, Sigma_wf, Epsilon_wf, etc. Options are:
    • 0: PAIR_LJ12_6_CS: Cut and shifted 12-6 Lennard-Jones potential.
    • 1: PAIR_COULOMB_CS: Cut and shifted Coulomb (note ... this is generally a bad idea - turn on Type_coul instead to preserve charge neutrality.
    • 2: PAIR_COULOMB: Full Coulomb potential used in forming integration stencils. (note ... this is still approximate and a bad idea - again turn on Type_coul instead to preserve charge neutrality.
    • 3: PAIR_YUKAWA_CS: Cut and shifted Yukawa potential (defined as in Egorov, Phys.Rev.E., v.70, p.031402, 2004).
  • Ipot_ww_n[Nwall_type][Nwall_type](int array): An array of switches indicating whether Tramonto should compute the type of neutral interactions between pairs of surface types in the system (only available for atomic surfaces). Often these terms are ignored; however, they may be needed in some cases. One example is the calculation of the potential of mean force between two solvated atoms, molecules, colloidal particles, or surfaces requires the direct interaction between a pair of explicit surfaces. Entries should be: O=FALSE, 1=TRUE; however, the parameters can be set more rapidly using the following convention:
    • -2 in first entry of array turns off these terms for entire array (don't compute any uww).
    • -1 in first entry of array turns on these terms for entire array (compute uww for all surface pairs).
  • Type_uwwPot(int): Select form for 3D surface-surface interaction potentials in the problem. Note that at the time of the v2.1 release this parameter is not dependent on the surface type, and all wall-wall potentials must have the same functional form. Choices are identical to Type_pairPot; however, the interaction potential parameters here are all based on wall-wall parameters, Sigma_ww, Epsilon_ww, etc. Options are:
    • 0: PAIR_LJ12_6_CS: Cut and shifted 12-6 Lennard-Jones potential.
    • 1: PAIR_COULOMB_CS: Cut and shifted Coulomb (note ... this is generally a bad idea - turn on Type_coul instead to preserve charge neutrality.
    • 2: PAIR_COULOMB: Full Coulomb potential used in forming integration stencils. (note ... this is still approximate and a bad idea - again turn on Type_coul instead to preserve charge neutrality.
    • 3: PAIR_YUKAWA_CS: Cut and shifted Yukawa potential (defined as in Egorov, Phys.Rev.E., v.70, p.031402, 2004).