surface tension and widom particle insertion (WIP)

src/widom.rs

@@ -0,0 +1,138 @@
+mod trajectory;
+use trajectory::*;
+mod energy;
+use energy::*;
+extern crate rand;
+use rand::Rng;
+
+const LJ_EPS : f64 = 1.0;
+const LJ_SIG : f64 = 1.0;
+
+static MKSA_PLANCKS_CONSTANT_H : f64 = 1.0;
+static MASS : f64 = 1.0;
+
+const INSERTIONS_PER_STEP : usize = 10;
+const RUN_AVG_SIZE : usize = 100;
+
+const SHIFT : bool = true;
+
+// returns number of particles in liquid and gas phase as tuble
+fn count_particles(rz: &[f64], num_particles: usize, liquid_height: f64) -> (usize, usize) {
+    let mut liquid_count = 0;
+    let mut gas_count = 0;
+    for i in 0..num_particles {
+        if rz[i] < liquid_height { liquid_count += 1; }
+        else { gas_count += 1; }
+    }
+    return (liquid_count, gas_count);
+}
+
+fn get_particle_insertion_energy(rx: &[f64], ry: &[f64], rz: &[f64], num_particles: usize, x: f64, y: f64, z: f64, l_x: f64,l_y: f64, l_z: f64, cutoff_sqr: f64, e_shift: f64) -> f64 {
+    let mut energy = 0.0;
+    let half_l_x = l_x/2.0;
+    let half_l_y = l_y/2.0;
+    let half_l_z = l_z/2.0;
+    for i in 0..num_particles {
+
+        let dist_squared = get_particle_distance_squared(x, y, z, rx[i],ry[i],rz[i], l_x, l_y, l_z, half_l_x, half_l_y, half_l_z);
+        if dist_squared < cutoff_sqr {
+            let (e,v) = eval_pair_energy(dist_squared, e_shift);
+            energy += e;
+        }
+    }
+    return energy;
+}
+
+fn main() {
+
+    let mut trj_reader = TrjReader::new(&"2phases/10k_1step.xyz".to_string());
+    let mut frame = trj_reader.next_frame();
+
+    let volume = frame.box_x * frame.box_y * frame.box_z;
+    let beta = 1.0/frame.temperature;
+    let cutoff_sqr = frame.lj_cutoff * frame.lj_cutoff;
+
+    let mut gas_slab = 2.0;
+    let mut liquid_height = frame.box_z / (gas_slab + 1.0);
+    let liquid_volume = volume / (gas_slab + 1.0);
+    let gas_volume = volume - liquid_volume;
+
+    let wave = MKSA_PLANCKS_CONSTANT_H / (2.0 * std::f64::consts::PI * MASS * frame.temperature / frame.lj_eps).sqrt();
+
+
+    let mut rng = rand::thread_rng();
+
+    let e_shift = if SHIFT { 4.0 * LJ_EPS * ( (LJ_SIG/frame.lj_cutoff).powi(12) - (LJ_SIG/frame.lj_cutoff).powi(6) ) } else { 0.0 };
+
+    let mut frame_count = 0;
+    let mut widom_sum_gas = 0.0;
+    let mut ideal_sum_gas = 0.0;
+    let mut widom_sum_liquid = 0.0;
+    let mut ideal_sum_liquid = 0.0;
+
+    let mut avg_count = 0;
+    loop  {
+        frame_count += 1;
+        avg_count += 1;
+
+
+        // test particle liquid energy
+        let lx = frame.box_x * rng.gen::<f64>();
+        let ly = frame.box_y * rng.gen::<f64>();
+        let lz = liquid_height * rng.gen::<f64>();
+        let widom_e_liquid = get_particle_insertion_energy(&frame.rx, &frame.ry, &frame.rz, frame.num_particles, lx, ly, lz, frame.box_x, frame.box_y, frame.box_z, cutoff_sqr, e_shift);
+        widom_sum_liquid += (-beta*widom_e_liquid).exp();
+
+        // test particle gas energy
+        let gx = frame.box_x * rng.gen::<f64>();
+        let gy = frame.box_y * rng.gen::<f64>();
+        let gz = ((frame.box_z - liquid_height) * rng.gen::<f64>()) + liquid_height;
+        let widom_e_gas = get_particle_insertion_energy(&frame.rx, &frame.ry, &frame.rz, frame.num_particles, gx, gy, gz, frame.box_x, frame.box_y, frame.box_z, cutoff_sqr, e_shift);
+        widom_sum_gas += (-beta*widom_e_gas).exp();
+
+        // calculate number of particles in each phase
+        let mut liquid_count = 0.0;
+        let mut gas_count = 0.0;
+        for i in 0..frame.num_particles {
+            if frame.rz[i] < liquid_height { liquid_count += 1.0; }
+            else { gas_count += 1.0; }
+        }
+
+        // calculate ideal gas potential for both phases
+        let wave = MKSA_PLANCKS_CONSTANT_H / (2.0 * std::f64::consts::PI * MASS * frame.temperature / frame.lj_eps).sqrt();
+        ideal_sum_gas += frame.temperature / frame.lj_eps * (gas_volume/(wave.powi(3)* gas_count)).ln();
+        ideal_sum_liquid += frame.temperature / frame.lj_eps * (liquid_volume/(wave.powi(3)* liquid_count)).ln();
+
+
+
+        if avg_count == RUN_AVG_SIZE {
+            let ideal_gas = ideal_sum_gas / avg_count as f64;
+            let ideal_liquid = ideal_sum_liquid / avg_count as f64;
+            let excess_gas = -(widom_sum_gas/avg_count as f64).ln()/beta;
+            let excess_liquid = -(widom_sum_liquid/avg_count as f64).ln()/beta;
+            println!("Frame {}   gas {}   liquid {}  particlecount:{}/{}", frame_count, ideal_gas + excess_gas, ideal_liquid + excess_liquid, gas_count, liquid_count);
+            avg_count = 0;
+            ideal_sum_gas = 0.0;
+            ideal_sum_liquid = 0.0;
+            widom_sum_gas = 0.0;
+            widom_sum_liquid = 0.0;
+
+        }
+
+        //            liquid_gas_sum = 0.0;
+        //            excess_liquid_sum = 0.0;
+        //            gas_gas_sum = 0.0;
+        //            excess_gas_sum = 0.0;
+        //            avg_count = 0;
+
+
+
+
+        if !trj_reader.update_with_next(&mut frame) { break }
+    }
+
+
+
+
+
+}