A 50:50 binary Lennard-Jones mixture is quenched below its critical solution temperature. Same-species attractions (epsilon_AA = epsilon_BB = 1.0) are stronger than cross-species (epsilon_AB = 0.5), driving spontaneous phase separation via spinodal decomposition. Composition fluctuations amplify and coarsen into macroscopic A-rich and B-rich domains — the same mechanism underlying biomolecular condensate formation in cells. The domain growth follows the Lifshitz-Slyozov t^(1/3) scaling law.
Atoms2,048
T (final)0.710
PE/atom-0.002
P (final)1.3
Snapshots41
Runtime8.4s
LAMMPS Input File · spinodal.in
1 # Spinodal decomposition: 50:50 binary LJ mixture quenched below T_c
2 # Same-species attractions are stronger than cross-species, driving
3 # spontaneous phase separation.
4
5 units lj
6 atom_style atomic
7 dimension 3
8 boundary p p p
9
10 lattice fcc 0.85
11 region box block 0 8 0 8 0 8
12 create_box 2 box
13 create_atoms 1 box
14 mass 1 1.0
15 mass 2 1.0
16
17 # Randomly relabel half the atoms as type 2 (50:50 mixture)
18 set type 1 type/fraction 2 0.5 48392
19
20 pair_style lj/cut 2.5
21 pair_coeff 1 1 1.0 1.0 2.5 # A-A attraction
22 pair_coeff 2 2 1.0 1.0 2.5 # B-B attraction
23 pair_coeff 1 2 0.5 1.0 2.5 # A-B weaker -> demixing
24 pair_modify shift yes
25
26 velocity all create 2.0 87287 dist gaussian
27 timestep 0.005
28
29 # NVT well below the consolute temperature
30 fix integ all nvt temp 0.7 0.7 0.5
3D Particle Viewer
Thermodynamics
The Kremer-Grest model is the foundation of computational polymer physics. 36 chains of 20 beads each interact via a purely repulsive WCA potential (shifted LJ with cutoff at 2^(1/6) sigma) and are connected by finitely extensible nonlinear elastic (FENE) bonds. Starting from straight-rod configurations, the chains rapidly randomize into a disordered melt. This model captures universal polymer dynamics — Rouse relaxation, reptation, and entanglement — and is widely used to study polymer blends, gels, and biomolecular assemblies.
Atoms720
T (final)1.008
PE/atom0.027
P (final)0.0
Snapshots41
Runtime0.4s
LAMMPS Input File · polymer.in
1 # Kremer-Grest polymer melt: bead-spring chains with FENE bonds.
2 # 36 chains of 20 beads each; WCA repulsion + FENE bonds.
3
4 units lj
5 atom_style bond
6 dimension 3
7 boundary p p p
8
9 read_data polymer_melt.data
10
11 # Purely repulsive Weeks-Chandler-Andersen potential
12 pair_style lj/cut 1.122462
13 pair_coeff 1 1 1.0 1.0 1.122462
14 pair_modify shift yes
15
16 # Finitely extensible nonlinear elastic bonds
17 bond_style fene
18 bond_coeff 1 30.0 1.5 1.0 1.0
19 special_bonds fene
20
21 velocity all create 1.0 87287 dist gaussian
22 timestep 0.005
23
24 fix integ all nvt temp 1.0 1.0 0.5
3D Particle Viewer
Thermodynamics
A dense Lennard-Jones liquid slab is placed in the center of an elongated simulation box with vacuum above and below. At T=0.85 (well below the critical temperature T_c ~ 1.3), the system maintains stable liquid-vapor coexistence. The pair cutoff is extended to 3.5 sigma to capture long-range interactions that determine surface tension. The interfaces exhibit thermal capillary fluctuations, and occasional atoms evaporate into the vapor phase. This geometry is the standard method for computing surface tension via the pressure tensor anisotropy: gamma = L_z/2 * (P_N - P_T).
Atoms2,688
T (final)0.861
PE/atom-0.002
P (final)-0.0
Snapshots36
Runtime15.5s
LAMMPS Input File · slab.in
1 # Liquid-vapor slab: dense LJ liquid sandwiched between vacuum.
2 # Long cutoff captures surface tension via pressure tensor anisotropy.
3
4 units lj
5 atom_style atomic
6 dimension 3
7 boundary p p p
8
9 lattice fcc 0.84
10 region box block 0 8 0 8 0 30
11 region slab block 0 8 0 8 10 20
12 create_box 1 box
13 create_atoms 1 region slab
14 mass 1 1.0
15
16 pair_style lj/cut 3.5
17 pair_coeff 1 1 1.0 1.0
18
19 velocity all create 0.85 87287 dist gaussian
20 timestep 0.005
21
22 # Stable liquid-vapor coexistence at T=0.85 (well below T_c ~ 1.3)
23 fix integ all nvt temp 0.85 0.85 0.5
3D Particle Viewer
Thermodynamics
Two spherical Lennard-Jones nanoparticles (radius ~ 5 sigma, ~500 atoms each) are placed with a small gap between them. At moderate temperature (T=0.4), surface atoms diffuse across the gap, forming a neck that grows over time as the system minimizes its total surface energy. This sintering process is fundamental to powder metallurgy, nanoparticle synthesis, and additive manufacturing. The shrinking boundary box visible in the viewer is an artifact of the non-periodic boundaries (shrink-wrapped).
Atoms1,042
T (final)0.394
PE/atom-0.005
P (final)0.0
Snapshots36
Runtime2.6s
LAMMPS Input File · sinter.in
1 # Nanoparticle sintering: two crystalline LJ clusters merging.
2 # Shrink-wrapped boundary; surface diffusion forms a neck over time.
3
4 units lj
5 atom_style atomic
6 dimension 3
7 boundary s s s
8
9 lattice fcc 1.0
10 region box block -2 24 -2 24 -2 24
11 create_box 1 box
12
13 # Two spherical clusters separated by a small gap
14 region sphere1 sphere 7 11 11 5 units box
15 region sphere2 sphere 17 11 11 5 units box
16 create_atoms 1 region sphere1
17 create_atoms 1 region sphere2
18 mass 1 1.0
19
20 pair_style lj/cut 2.5
21 pair_coeff 1 1 1.0 1.0
22 pair_modify shift yes
23
24 velocity all create 0.4 87287 dist gaussian
25 timestep 0.005
26
27 fix integ all nvt temp 0.4 0.4 0.5
3D Particle Viewer
Thermodynamics
