Description of the program Atomc: Monte Carlo simulation of atomic fluids in the (T,V,N), (T,P,N), or (T,V,mu) ensemble

Mihaly Mezei

Department of Pharmacological Sciences,

Icahn School of Medicine at Mount Sinai

New York, NY 10029

June 23, 2004

I. General description
II. Installation
III. Input syntax
IV. Sample input
V. File formats
VI. References

I. General Description

Atomc is a Metropolis Monte Carlo program for the simulation of atomic fluids. The first atom can be different from the rest.

The simulations can be performed in the (T,V,N), (T,P,N) or (T,V,mu) ensembles. In the (T,V,N) ensemble, force biased displacements REF or energy-scaled displacements REF can be used. In the (T,P,N) ensemble, virial-biased volume changes REF can be used. In the (T,V,mu) ensemble, cavity-biased insertions REF can be used.

II. Installation

The program is written in standard Fortran-77. Before compilation, certain symbols have to be changed in the source file atomc.for. There is a Fortran-77 preprocessor program pre.f that performs the dimension-related substitution. It can be edited to accomodate the system to be simulated. After compilation it asks for the source file name without the .for (i.e., atomc and then read the file atomc.for, make the substitutions and create a file atomc.f that is ready to be compiled.

The symbols changed by the preprocessor determine the maximum dimensions of arrays used. The symbols prefixed by # are replaced by numbers as follows

Furthermore, certain platform-dependent lines may be uncommented as follows:

II. Input syntax

The input format is specified using standard Fortran FORMATs. For example, (24i3,a4) describes the input of 24 integers of 3 digits in one line (right-adjusted), followed by a string of 4 characters; (5f8.0,10x,e12.5) describes the input of five real numbers, occupying 8 spaces each, with the decimal point explicitly given, followed by 10 spaces to be skipped and after that a number in scientific notation, occupying 12 spaces with a 5-digit mantissa, e.g., -1.76921E-03. The appearance of / in the format instructs the input to start to read a new line.

  1. Option array : iop (40i2)

    If iop(10) > 0 (run continued from a checkpoint file), skip items 2-10.

  2. id (20a4/20a4)
  3. natoms, ndim, temp, edge, pext, ba, cutof, cedgs, fblam (2i5,7f10.0)
  4. delvol, vlam (10x,7f10.0)
  5. ntry, natxp, ngrid, rsph (3i5,6f10.0)
  6. aesd, gexplim, batan,epmav (10x,7f10.0)
  7. if iop(1) = 2: ktiexp, ljavg, epsslt, sigslt, epsslv, sigslv, cplp (2i5, 5f10.0)
  8. nmcmax, nmcvid, nmovrp, nvidrp, nmcsav, nmcrec, nmcplt (8i10)
  9. rdmx, ri, rfsl, ebemin, ebegrid (5f15.10)
  10. For Widom insertion method calculations (iop(14)=1): ntry, eftmin, eftgrd (i5,5x,7f10.0)

    When iop(10)=0, the input termintes here.

  11. nmcmax, nmcvid, nmovrp, nvidrp (8i10)

IV. Sample input

 2 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0                                   0 1 0

  100    3  1.0        5.5       0.0      0.0     2.5       0.3        0.5
    2    0  1.0        1.0        1.0      1.0      1.0
     20000       100      1000      100      25000      5000    200000

V. File formats

VI. References