Docs/fix lb multicomponent #4
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akgokulraman
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Dec 2, 2025
akgokulraman
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Dec 3, 2025
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| * **film** *thickness* *C1_film* *C2_film*: Creates a horizontal film of specified thickness (as a fraction of the box height) centered in the simulation box with composition C1_film, C2_film, C3_film = 1 - C1_film - C2_film, surrounded by bulk mixture. Small random fluctuations (±0.01) are added to seed phase separation. | ||
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| * **mixed_droplet** *radius* *C1_drop* *C2_drop*: Creates a ternary droplet with specified radius and composition (C1_drop, C2_drop, C3_drop = 1 - C1_drop - C2_drop) surrounded by pure C3 solvent. Small random fluctuations (±0.01) are added within the droplet. |
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| * **mixed_droplet** *radius* *C1_drop* *C2_drop*: Creates a ternary droplet with specified radius and composition (C1_drop, C2_drop, C3_drop = 1 - C1_drop - C2_drop) surrounded by pure C3 solvent. Small random fluctuations (±0.01) are added within the droplet. | |
| * **mixed_droplet** *radius* *C1_drop* *C2_drop*: Creates a ternary droplet with specified radius and composition (C1_drop, C2_drop, C3_drop = 1 - C1_drop - C2_drop) surrounded by component 3 in bulk. |
akgokulraman
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Dec 3, 2025
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| * **mixed_droplet** *radius* *C1_drop* *C2_drop*: Creates a ternary droplet with specified radius and composition (C1_drop, C2_drop, C3_drop = 1 - C1_drop - C2_drop) surrounded by pure C3 solvent. Small random fluctuations (±0.01) are added within the droplet. | ||
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| .. math:: |
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| .. math:: |
akgokulraman
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| * **mixed_droplet** *radius* *C1_drop* *C2_drop*: Creates a ternary droplet with specified radius and composition (C1_drop, C2_drop, C3_drop = 1 - C1_drop - C2_drop) surrounded by pure C3 solvent. Small random fluctuations (±0.01) are added within the droplet. | ||
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| .. math:: | ||
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akgokulraman
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Dec 3, 2025
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| .. math:: | ||
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| \text{subNbx} = \frac{N_x}{P_x} + 2h_x \\ |
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| \text{subNbx} = \frac{N_x}{P_x} + 2h_x \\ |
akgokulraman
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Dec 3, 2025
| .. math:: | ||
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| \text{subNbx} = \frac{N_x}{P_x} + 2h_x \\ | ||
| \text{subNby} = \frac{N_y}{P_y} + 2h_y \\ |
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| \text{subNby} = \frac{N_y}{P_y} + 2h_y \\ |
akgokulraman
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Dec 3, 2025
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| \text{subNbx} = \frac{N_x}{P_x} + 2h_x \\ | ||
| \text{subNby} = \frac{N_y}{P_y} + 2h_y \\ | ||
| \text{subNbz} = \frac{N_z}{P_z} + 2h_z |
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| \text{subNbz} = \frac{N_z}{P_z} + 2h_z |
akgokulraman
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| \text{subNby} = \frac{N_y}{P_y} + 2h_y \\ | ||
| \text{subNbz} = \frac{N_z}{P_z} + 2h_z | ||
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| where hₓ = hᵧ = hᵤ = 2 is the halo extent required for gradient and Laplacian calculations. |
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| where hₓ = hᵧ = hᵤ = 2 is the halo extent required for gradient and Laplacian calculations. |
akgokulraman
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| This fix accepts several internal parameters that control the thermodynamic and transport properties: | ||
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| * **tau_r**, **tau_p**, **tau_s**: Relaxation times for momentum transport and order parameter transport. These control the viscosity and diffusivity of the fluid components. |
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| * **tau_r**, **tau_p**, **tau_s**: Relaxation times for momentum transport and order parameter transport. These control the viscosity and diffusivity of the fluid components. | |
| * **tau_r**, **tau_p**, **tau_s**: Relaxation times for momentum transport and order parameter transport. |
akgokulraman
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| * **tau_r**, **tau_p**, **tau_s**: Relaxation times for momentum transport and order parameter transport. These control the viscosity and diffusivity of the fluid components. | ||
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| * **gamma_p**, **gamma_s**: Mobility coefficients controlling the rate of change of the phase variables φ and ψ. |
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| * **gamma_p**, **gamma_s**: Mobility coefficients controlling the rate of change of the phase variables φ and ψ. | |
| * **gamma_p**, **gamma_s**: Parameters controlling the mobility of the phases $\phi$ and $\psi$. |
akgokulraman
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| .. math:: | ||
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| \gamma_{mn} = \frac{\sqrt{(\kappa_m + \kappa_n)(\lambda_m + \lambda_n)}}{6} |
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| \gamma_{mn} = \frac{\sqrt{(\kappa_m + \kappa_n)(\lambda_m + \lambda_n)}}{6} | |
| \gamma_{mn} = \frac{\alpha}{6}\left(\kappa_m + \kappa_n\right) |
akgokulraman
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| \gamma_{mn} = \frac{\sqrt{(\kappa_m + \kappa_n)(\lambda_m + \lambda_n)}}{6} | ||
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| * **alpha**: Gradient energy coefficient. |
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| * **alpha**: Gradient energy coefficient. | |
| * **alpha**: Parameter correlated with the interface width in LB units. The interface width is given by 4*alpha. |
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| The *dumpxdmf* keyword enables output of the fluid fields to files that can be visualized using Paraview or other XDMF-compatible visualization software. The output includes: | ||
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| * Density field ρ (converted to physical units) | ||
| * Order parameters φ and ψ (converted to physical units) |
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| * Order parameters φ and ψ (converted to physical units) | |
| * Order parameters \phi and \psi |
akgokulraman
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| The *dumpxdmf* keyword enables output of the fluid fields to files that can be visualized using Paraview or other XDMF-compatible visualization software. The output includes: | ||
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| * Density field ρ (converted to physical units) |
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| * Density field ρ (converted to physical units) | |
| * Density field ρ |
akgokulraman
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| * Density field ρ (converted to physical units) | ||
| * Order parameters φ and ψ (converted to physical units) | ||
| * Pressure field p (converted to physical units) |
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| * Pressure field p (converted to physical units) | |
| * Pressure field p |
akgokulraman
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| * Density field ρ (converted to physical units) | ||
| * Order parameters φ and ψ (converted to physical units) | ||
| * Pressure field p (converted to physical units) | ||
| * Velocity field **u** (converted to physical units) |
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| * Velocity field **u** (converted to physical units) | |
| * Velocity vector field **u** |
akgokulraman
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| **Output** | ||
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| The *dumpxdmf* keyword enables output of the fluid fields to files that can be visualized using Paraview or other XDMF-compatible visualization software. The output includes: |
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| The *dumpxdmf* keyword enables output of the fluid fields to files that can be visualized using Paraview or other XDMF-compatible visualization software. The output includes: | |
| The *dumpxdmf* keyword enables output of the fluid fields to files that can be visualized using Paraview or other XDMF-compatible visualization software. The output (in LB units) includes: |
akgokulraman
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Dec 3, 2025
| * A text .xdmf file containing metadata and grid structure | ||
| * A binary .raw file containing the actual field data | ||
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| The concentration fields can be recovered from the output using: |
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| The concentration fields can be recovered from the output using: |
akgokulraman
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Dec 3, 2025
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| .. math:: | ||
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| C_1 = \frac{\rho + \phi}{2}, \quad C_2 = \frac{\rho - \phi}{2}, \quad C_3 = \psi |
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| C_1 = \frac{\rho + \phi}{2}, \quad C_2 = \frac{\rho - \phi}{2}, \quad C_3 = \psi |
akgokulraman
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Dec 3, 2025
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| The concentration fields can be recovered from the output using: | ||
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| .. math:: |
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| .. math:: |
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| **Boundary Conditions** | ||
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| The ternary lattice-Boltzmann implementation currently supports periodic boundary conditions in all three directions. The boundary conditions are specified through the main LAMMPS :doc:`boundary <boundary>` command and must be set to periodic (p p p) for proper operation. |
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| The ternary lattice-Boltzmann implementation currently supports periodic boundary conditions in all three directions. The boundary conditions are specified through the main LAMMPS :doc:`boundary <boundary>` command and must be set to periodic (p p p) for proper operation. | |
| The ternary lattice-Boltzmann implementation currently only supports periodic boundary conditions in all three directions. The boundary conditions are specified through the main LAMMPS :doc:`boundary <boundary>` command and must be set to periodic (p p p) for proper operation. |
akgokulraman
reviewed
Dec 3, 2025
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| The ternary lattice-Boltzmann implementation currently supports periodic boundary conditions in all three directions. The boundary conditions are specified through the main LAMMPS :doc:`boundary <boundary>` command and must be set to periodic (p p p) for proper operation. | ||
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| *Periodic Boundaries* |
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| *Periodic Boundaries* |
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| *Periodic Boundaries* | ||
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| With periodic boundary conditions, the fluid domain wraps around in all directions. The distribution functions that stream out of one side of the simulation box re-enter from the opposite side. This is handled automatically through the MPI communication scheme, which includes a halo region of 2 lattice layers on each side of the local processor subdomain. |
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| With periodic boundary conditions, the fluid domain wraps around in all directions. The distribution functions that stream out of one side of the simulation box re-enter from the opposite side. This is handled automatically through the MPI communication scheme, which includes a halo region of 2 lattice layers on each side of the local processor subdomain. |
akgokulraman
reviewed
Dec 3, 2025
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| With periodic boundary conditions, the fluid domain wraps around in all directions. The distribution functions that stream out of one side of the simulation box re-enter from the opposite side. This is handled automatically through the MPI communication scheme, which includes a halo region of 2 lattice layers on each side of the local processor subdomain. | ||
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| The halo communication ensures that: |
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| The halo communication ensures that: |
akgokulraman
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Dec 3, 2025
| *Periodic Boundaries* | ||
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| With periodic boundary conditions, the fluid domain wraps around in all directions. The distribution functions that stream out of one side of the simulation box re-enter from the opposite side. This is handled automatically through the MPI communication scheme, which includes a halo region of 2 lattice layers on each side of the local processor subdomain. | ||
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akgokulraman
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Dec 3, 2025
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| The halo communication ensures that: | ||
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| * Gradient calculations (∇ρ, ∇φ, ∇ψ) required for the chemical potentials can be performed correctly near subdomain boundaries |
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| * Gradient calculations (∇ρ, ∇φ, ∇ψ) required for the chemical potentials can be performed correctly near subdomain boundaries |
akgokulraman
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Dec 3, 2025
| The halo communication ensures that: | ||
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| * Gradient calculations (∇ρ, ∇φ, ∇ψ) required for the chemical potentials can be performed correctly near subdomain boundaries | ||
| * Laplacian calculations (∇²ρ, ∇²φ, ∇²ψ) have access to necessary neighbor information |
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| * Laplacian calculations (∇²ρ, ∇²φ, ∇²ψ) have access to necessary neighbor information |
akgokulraman
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Dec 3, 2025
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| * Gradient calculations (∇ρ, ∇φ, ∇ψ) required for the chemical potentials can be performed correctly near subdomain boundaries | ||
| * Laplacian calculations (∇²ρ, ∇²φ, ∇²ψ) have access to necessary neighbor information | ||
| * Streaming of distribution functions across processor boundaries is handled correctly |
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| * Streaming of distribution functions across processor boundaries is handled correctly |
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Co-authored-by: Gokul Raman <[email protected]>
Co-authored-by: Gokul Raman <[email protected]>
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Adds new documentation file fix_lb_multicomponent.rst describing the ternary lattice Boltzmann model implemented in fix_lb_multicomponent.cpp.
This fix extends fix_lb_fluid to support three-component mixtures, following the work by Arumugam Kumar et al. (2024).
Related Issue(s)
N/A – new documentation entry for existing code developed under Schiller Lab.
Author(s)
Rasib Zaman ([email protected]
), Schiller Lab – University of Delaware
Licensing
I agree that my contribution will be included in LAMMPS and redistributed under GPL v2 / LGPL v2.1.
Backward Compatibility
No changes to code or input behavior — documentation only.
Implementation Notes
Documentation tested with the LAMMPS Sphinx build system and formatted consistently with existing fix_lb_fluid.rst.
Post Submission Checklist
Documentation is still in progress
Licensing information is complete
The doc file builds correctly with the LAMMPS documentation system