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fort.57 file — MM energy minimization report

The fort.57 file contains a detailed report of a molecular mechanics (MM) energy minimization performed by ReaxFF.

It is written during MM runs, typically using a conjugate-gradient minimizer, and provides iteration-by-iteration information on energy convergence and force reduction.

Purpose of the fort.57 file

The fort.57 output is primarily used to:

  • Monitor energy minimization convergence
  • Track reduction of atomic forces (RMSG)
  • Diagnose minimizer behavior and stability
  • Verify termination criteria for MM runs

When fort.57 is generated

  • Generated during MM minimization runs (imetho = 1 or 2)
  • Updated every MM iteration
  • May be deleted automatically if control keyword iout5 = 1

File structure

The file consists of:

  1. A structure identifier
  2. A tabular iteration log

Column definitions

Each iteration line contains the following columns:

Column Description
Iter. MM iteration number
Epot Potential energy (kcal/mol)
Max.move Maximum atomic displacement in this iteration
Factor Scaling factor used by the minimizer
RMSG Root-mean-square gradient of forces
nfc Number of force calculations

Example 3.3: fort.57 output file

Ethyl_radical

Iter. Epot Max.move Factor RMSG nfc
0 -664.0048203101 0.000000 0.500000 4.969706 0
1 -664.0170216413 15.795587 0.089117 3.360058 0
2 -664.0394728751 9.339616 0.135649 6.279516 0
3 -664.0765683298 0.001387 1.957694 3.047916 0
4 -664.0956555161 0.000342 3.000000 2.270724 0
5 -664.1009627083 0.001933 0.585262 1.026026 0
6 -664.1025221864 0.000851 1.000000 0.465193 0

Interpreting the output

Key quantities

  • Epot
    Potential energy of the system at each iteration. A monotonic decrease usually indicates stable minimization.

  • RMSG
    Root-mean-square gradient of the forces. This is the primary convergence metric.

Termination criteria

An MM minimization terminates when either:

  • RMSG drops below the threshold defined by endmm in the control file, or
  • The maximum number of iterations (maxit in control) is reached

In Example 3.3, the run terminates when RMSG < 0.500.

Practical notes

  • fort.57 is the MM analogue of fort.73/energylog for MD
  • Useful for diagnosing poor initial geometries
  • Sudden spikes in Max.move or RMSG may indicate unstable force-field parameters
  • Often parsed automatically in force-field optimization workflows

Summary

  • fort.57 reports MM minimization progress
  • Focus on Epot and RMSG for convergence assessment
  • Termination controlled by endmm and maxit
  • Essential for validating MM geometry relaxations