10. Results and Analysis

10.1. Result-directory naming

output_folder is a base name. PhonoMC scans sibling directories and creates the next numeric suffix, for example Cross_100nm_0 followed by Cross_100nm_1. Record the exact printed result path in batch workflows.

10.2. convergence.txt

The header begins with # and defines all columns. The current columns are:

timestep

Completed solver step.

time_ps

Simulated elapsed time in ps.

T_1 ... T_n

Grid temperatures in K, in the same index order as grid_centers.csv.

heatflux

Particle-weighted average heat flux along the inferred transport axis in W/m².

kappa_int

Conductivity from a least-squares grid-temperature gradient.

kappa_eff

Conductivity from reservoir endpoint temperatures and full domain length.

absorbed, injected, recovered, net

Per-step reservoir and recovery bookkeeping. net is reservoir injection minus absorption.

hs_injected / hs_injected_energy_ev

Local-heat-source particle count and injected energy for the step.

10.3. Temperature convergence

Look for a statistically stationary profile rather than a perfectly flat trace. Increase simulation time if the profile is still drifting. Increase particle count if the steady trace is dominated by noise.

For a nominally one-dimensional case, plot several representative T_i traces and inspect the final spatial profile using grid_centers.csv.

10.4. Particle balance

Reservoir-driven steady cases should not exhibit a persistent unexplained particle drift. Compare cumulative absorption and injection in summary.txt and inspect recovered events. Frequent recovery indicates a geometry or collision-tolerance problem, not a normal convergence mechanism.

10.5. Conductivity interpretation

Compare kappa_int and kappa_eff after the temperature profile has settled. Differences can arise from boundary jumps, nonlinearity, insufficient grid resolution, or sampling noise.

Repeat a conductivity calculation with:

  • more particles

  • a smaller time step

  • longer simulated time

  • at least one finer grid

Report the convergence study alongside the selected conductivity value.

10.6. summary.txt diagnostics

The summary includes normalized input, geometry, grid and boundary counts, runtime, OpenMP settings, rough-scattering selection statistics, escaped particle recovery, reservoir totals, and heat-source injection totals.

Large rough-boundary fallback counts deserve investigation. They can indicate that no frequency-compatible reflected mode was available for many events.

10.7. One-dimensional plots

python3 tools/plot_convergence.py RESULT_DIRECTORY \
  --max-temp-lines 40 --show-legend

Outputs:

  • plots_1d/temperature_vs_time.png

  • plots_1d/heatflux_vs_time.png

  • plots_1d/kappa_vs_time.png

10.8. Three-dimensional plots

python3 tools/plot_temperature_3d.py \
  --input INPUT.toml \
  --results RESULT_DIRECTORY \
  --x-slice-rel 0.5 \
  --y-slice-rel 0.5

Use slice images to check whether the heat-source region, periodic directions, and thermal contacts produce the intended spatial pattern.