Skip to content

fort.73 file — MD partial energy decomposition

The fort.73 file contains a partial energy contribution report from a ReaxFF molecular dynamics (MD) simulation.

It provides a detailed breakdown of the total potential energy into its individual physical components and is the MD analogue of fort.58 (which is written during MM minimization).

Purpose of the fort.73 file

fort.73 is used to:

  • Analyze which interaction terms dominate during MD
  • Track how energy components evolve with time
  • Verify energy consistency with fort.71
  • Diagnose instabilities or unphysical behavior in MD runs
  • Support force-field development and validation

Output frequency

The output frequency is controlled by the control-file keyword:

iout1

A line is written to fort.73 every iout1 MD iterations.

In Example 3.6, iout1 = 5.

File structure

  • One header line listing energy components
  • One data line per output step
  • Each row corresponds to the same MD iteration reported in fort.71

Energy components

All energies are reported in kcal/mol.

Column Description
Iter MD iteration number
Ebond Bond energy
Eatom Over- and undercoordination energy
Elp Lone-pair energy
Emol Molecular energy (not used in recent force fields)
Eval Valence angle energy
Ecoa Valence angle conjugation energy
Ehbo Hydrogen bond energy
Etors Torsion angle energy
Econj Torsion conjugation energy
Evdw van der Waals energy
Ecoul Coulomb (electrostatic) energy
Echarge Charge polarization energy

Example 3.6: fort.73 output file

Iter. Ebond Eatom Elp Emol Eval Ecoa Ehbo Etors Econj Evdw Ecoul Echarge

5  -905.00 -7.39 0.00 0.00 0.30 0.00 0.00 4.57 -0.49 255.78 -22.93 11.45
10 -913.27 -6.45 0.00 0.00 0.34 0.00 0.00 4.87 -0.51 262.72 -23.33 11.76
15 -915.74 -5.42 0.00 0.00 0.20 0.00 0.00 5.38 -0.53 263.86 -23.29 11.74
20 -910.80 -5.68 0.00 0.00 0.23 0.00 0.00 5.42 -0.53 258.94 -23.05 11.54
25 -907.76 -6.64 0.00 0.00 0.44 0.00 0.00 4.97 -0.51 257.35 -23.13 11.60
30 -910.68 -6.80 0.00 0.00 0.37 0.00 0.00 4.74 -0.51 260.62 -23.32 11.76
35 -914.36 -6.12 0.00 0.00 0.37 0.00 0.00 4.95 -0.53 263.46 -23.23 11.68
40 -910.62 -6.00 0.00 0.00 0.47 0.00 0.00 5.17 -0.53 259.26 -22.80 11.34
45 -906.77 -6.74 0.00 0.00 0.31 0.00 0.00 4.98 -0.51 256.49 -22.88 11.40

Relationship to fort.71

  • fort.73 contains all partial energy terms, including charge polarization energy
  • The sum of all energy components in fort.73 should equal:
Epot (from fort.71)

This makes fort.73 the most complete energy decomposition file produced during MD.

Practical notes

  • Sudden jumps in a single energy term often reveal the source of instability
  • Echarge is especially important in simulations with strong polarization effects
  • Commonly plotted alongside fort.71 for MD diagnostics
  • Widely used in automated ReaxKit analysis pipelines

Summary

  • fort.73 provides a full MD energy decomposition
  • Output frequency controlled by iout1
  • Energies sum to Epot in fort.71
  • Essential for energy analysis, validation, and force-field development