feat: refresh playground examples with 2D notebook demos

examples/pages/src/examples.ts

@@ -53,40 +53,75 @@ thermo          100
 run             5000`,
   },
   {
-    name: "LJ Cluster (large, 1M atoms)",
-    every: 10,
-    script: `# ~1,000,188 atoms (63^3 fcc cells x 4) — runs in a Web Worker so
-# the page stays responsive. Expect setup + 100 steps to take a few
-# minutes and several hundred MB of memory.
+    name: "Maxwell–Boltzmann distribution (2D)",
+    every: 100,
+    script: `# Give every atom the same speed in a random direction, then let
+# collisions do the rest: within a few hundred steps the velocity
+# distribution relaxes to the Maxwell–Boltzmann form (Boltzmann's
+# H-theorem in action). A 2D gas with the purely repulsive WCA
+# potential (LJ cut at its minimum) so energy stays kinetic.
 units           lj
-timestep        0.005
+dimension       2
 atom_style      atomic
-lattice         fcc 0.8442
-region          box block 0 63 0 63 0 63
+lattice         sq 0.3
+region          box block 0 32 0 32 -0.1 0.1
 create_box      1 box
 create_atoms    1 box
 mass            1 1.0
-velocity        all create 1.44 87287 loop geom
+pair_style      lj/cut 1.122462
+pair_coeff      1 1 1.0 1.0
+pair_modify     shift yes
+velocity        all create 1.0 777 dist gaussian
+variable        v0 equal 1.5
+variable        s  atom v_v0/sqrt(vx*vx+vy*vy)
+variable        ux atom vx*v_s
+variable        uy atom vy*v_s
+velocity        all set v_ux v_uy NULL
+neighbor        0.3 bin
+fix             1 all nve
+fix             2d all enforce2d
+thermo          200
+run             4000`,
+  },
+  {
+    name: "Condensation quench (2D)",
+    every: 200,
+    script: `# Take a hot 2D Lennard-Jones vapor and suddenly cool it below its
+# condensation point. The uniform gas becomes unstable, droplets
+# nucleate everywhere and then coarsen — a first-order phase
+# transition, with the potential energy tracking the latent heat.
+units           lj
+dimension       2
+atom_style      atomic
+lattice         sq 0.3
+region          box block 0 40 0 40 -0.1 0.1
+create_box      1 box
+create_atoms    1 box
+mass            1 1.0
+velocity        all create 1.0 8712 dist gaussian
 pair_style      lj/cut 2.5
 pair_coeff      1 1 1.0 1.0 2.5
 neighbor        0.3 bin
-neigh_modify    every 20 delay 0 check no
 fix             1 all nve
-thermo          10
-run             100`,
+fix             lang all langevin 1.0 1.0 1.0 3216
+fix             2d all enforce2d
+thermo          1000
+run             3000
+# quench: drop the thermostat target below the condensation point
+fix             lang all langevin 0.4 0.4 1.0 3216
+run             20000`,
   },
   {
-    name: "LJ Melt (KOKKOS, multithreaded)",
-    kokkos: true,
-    every: 200,
-    script: `# Runs on the KOKKOS (pthreads) build — pick a thread count in the
-# dropdown above and compare the performance summary at the end.
-# Styles get the /kk suffix automatically (-sf kk).
+    name: "LJ Cluster (large, 1M atoms)",
+    every: 10,
+    script: `# ~1,000,188 atoms (63^3 fcc cells x 4) — runs in a Web Worker so
+# the page stays responsive. Expect setup + 100 steps to take a few
+# minutes and several hundred MB of memory.
 units           lj
 timestep        0.005
 atom_style      atomic
 lattice         fcc 0.8442
-region          box block 0 12 0 12 0 12
+region          box block 0 63 0 63 0 63
 create_box      1 box
 create_atoms    1 box
 mass            1 1.0
@@ -96,8 +131,8 @@ pair_coeff      1 1 1.0 1.0 2.5
 neighbor        0.3 bin
 neigh_modify    every 20 delay 0 check no
 fix             1 all nve
-thermo          500
-run             10000`,
+thermo          10
+run             100`,
   },
   {
     name: "Energy Minimization",