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mc_npt_hs.f90
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! mc_npt_hs.f90
! Monte Carlo simulation, NPT ensemble, hard spheres
PROGRAM mc_npt_hs
!------------------------------------------------------------------------------------------------!
! This software was written in 2016/17 !
! by Michael P. Allen <[email protected]>/<[email protected]> !
! and Dominic J. Tildesley <[email protected]> ("the authors"), !
! to accompany the book "Computer Simulation of Liquids", second edition, 2017 ("the text"), !
! published by Oxford University Press ("the publishers"). !
! !
! LICENCE !
! Creative Commons CC0 Public Domain Dedication. !
! To the extent possible under law, the authors have dedicated all copyright and related !
! and neighboring rights to this software to the PUBLIC domain worldwide. !
! This software is distributed without any warranty. !
! You should have received a copy of the CC0 Public Domain Dedication along with this software. !
! If not, see <http://creativecommons.org/publicdomain/zero/1.0/>. !
! !
! DISCLAIMER !
! The authors and publishers make no warranties about the software, and disclaim liability !
! for all uses of the software, to the fullest extent permitted by applicable law. !
! The authors and publishers do not recommend use of this software for any purpose. !
! It is made freely available, solely to clarify points made in the text. When using or citing !
! the software, you should not imply endorsement by the authors or publishers. !
!------------------------------------------------------------------------------------------------!
! Takes in a configuration of atoms (positions)
! Cubic periodic boundary conditions
! Conducts Monte Carlo at given NPT (the temperature is irrelevant)
! Uses no special neighbour lists
! Reads several variables and options from standard input using a namelist nml
! Leave namelist empty to accept supplied defaults
! We take kT=1 throughout defining the unit of energy
! Positions r are divided by box length after reading in
! However, input configuration, output configuration, most calculations, and all results
! are given in simulation units defined by the model,
! in this case, for hard spheres, sigma = 1
! The logarithm of the box length is sampled uniformly
USE, INTRINSIC :: iso_fortran_env, ONLY : input_unit, output_unit, error_unit, iostat_end, iostat_eor
USE config_io_module, ONLY : read_cnf_atoms, write_cnf_atoms
USE averages_module, ONLY : run_begin, run_end, blk_begin, blk_end, blk_add
USE maths_module, ONLY : metropolis, random_translate_vector
USE mc_module, ONLY : introduction, conclusion, allocate_arrays, deallocate_arrays, &
& overlap_1, overlap, n, r
IMPLICIT NONE
! Most important variables
REAL :: box ! Box length
REAL :: dr_max ! Maximum MC displacement
REAL :: db_max ! Maximum MC box displacement
REAL :: pressure ! Specified pressure
INTEGER :: blk, stp, i, nstep, nblock, moves, ioerr
REAL, DIMENSION(3) :: ri
REAL :: box_scale, box_new, den_scale, delta, zeta, m_ratio, v_ratio
CHARACTER(len=4), PARAMETER :: cnf_prefix = 'cnf.'
CHARACTER(len=3), PARAMETER :: inp_tag = 'inp'
CHARACTER(len=3), PARAMETER :: out_tag = 'out'
CHARACTER(len=3) :: sav_tag = 'sav' ! May be overwritten with block number
NAMELIST /nml/ nblock, nstep, dr_max, db_max, pressure
WRITE( unit=output_unit, fmt='(a)' ) 'mc_npt_hs'
WRITE( unit=output_unit, fmt='(a)' ) 'Monte Carlo, constant-NPT'
CALL introduction
CALL RANDOM_SEED () ! Initialize random number generator
! Set sensible default run parameters for testing
nblock = 10
nstep = 10000
dr_max = 0.15
db_max = 0.005
pressure = 4.0
! Read run parameters from namelist
! Comment out, or replace, this section if you don't like namelists
READ ( unit=input_unit, nml=nml, iostat=ioerr )
IF ( ioerr /= 0 ) THEN
WRITE ( unit=error_unit, fmt='(a,i15)') 'Error reading namelist nml from standard input', ioerr
IF ( ioerr == iostat_eor ) WRITE ( unit=error_unit, fmt='(a)') 'End of record'
IF ( ioerr == iostat_end ) WRITE ( unit=error_unit, fmt='(a)') 'End of file'
STOP 'Error in mc_npt_hs'
END IF
! Write out run parameters
WRITE ( unit=output_unit, fmt='(a,t40,i15)' ) 'Number of blocks', nblock
WRITE ( unit=output_unit, fmt='(a,t40,i15)' ) 'Number of steps per block', nstep
WRITE ( unit=output_unit, fmt='(a,t40,f15.6)' ) 'Pressure', pressure
WRITE ( unit=output_unit, fmt='(a,t40,f15.6)' ) 'Maximum displacement', dr_max
WRITE ( unit=output_unit, fmt='(a,t40,f15.6)' ) 'Maximum box displacement', db_max
! Read in initial configuration and allocate necessary arrays
CALL read_cnf_atoms ( cnf_prefix//inp_tag, n, box ) ! First call just to get n and box
WRITE ( unit=output_unit, fmt='(a,t40,i15)' ) 'Number of particles', n
WRITE ( unit=output_unit, fmt='(a,t40,f15.6)' ) 'Simulation box length', box
CALL allocate_arrays ! Allocates r
CALL read_cnf_atoms ( cnf_prefix//inp_tag, n, box, r ) ! Second call to get r
r(:,:) = r(:,:) / box ! Convert positions to box units
r(:,:) = r(:,:) - ANINT ( r(:,:) ) ! Periodic boundaries
! Initial calculation and overlap check
IF ( overlap ( box ) ) THEN
WRITE ( unit=error_unit, fmt='(a)') 'Overlap in initial configuration'
STOP 'Error in mc_npt_hs'
END IF
! Initialize arrays for averaging and write column headings
m_ratio = 0.0
v_ratio = 0.0
CALL run_begin ( calc_variables() )
DO blk = 1, nblock ! Begin loop over blocks
CALL blk_begin
DO stp = 1, nstep ! Begin loop over steps
moves = 0
DO i = 1, n ! Begin loop over atoms
ri(:) = random_translate_vector ( dr_max/box, r(:,i) ) ! Trial move to new position (in box=1 units)
ri(:) = ri(:) - ANINT ( ri(:) ) ! Periodic boundary correction
IF ( .NOT. overlap_1 ( ri, i, box ) ) THEN ! Accept
r(:,i) = ri(:) ! Update position
moves = moves + 1 ! Increment move counter
END IF ! End accept
END DO ! End loop over atoms
m_ratio = REAL(moves) / REAL(n)
v_ratio = 0.0 ! Zero volume move counter
CALL RANDOM_NUMBER ( zeta ) ! Uniform random number in range (0,1)
zeta = 2.0*zeta - 1.0 ! Now in range (-1,+1)
box_scale = EXP ( zeta*db_max ) ! Sampling log(box) and log(vol) uniformly
box_new = box * box_scale ! New box (in sigma units)
den_scale = 1.0 / box_scale**3 ! Density scaling factor
IF ( .NOT. overlap ( box_new ) ) THEN ! Test for non-overlapping configuration
delta = pressure * ( box_new**3 - box**3 ) ! PV term (temperature = 1.0 )
delta = delta + REAL(n+1) * LOG(den_scale) ! Factor (n+1) consistent with log(box) sampling
IF ( metropolis ( delta ) ) THEN ! Accept Metropolis test
box = box_new ! Update box
v_ratio = 1.0 ! Set move counter
END IF ! reject Metropolis test
END IF ! End test for overlapping configuration
! Calculate and accumulate variables for this step
CALL blk_add ( calc_variables() )
END DO ! End loop over steps
CALL blk_end ( blk ) ! Output block averages
IF ( nblock < 1000 ) WRITE(sav_tag,'(i3.3)') blk ! Number configuration by block
CALL write_cnf_atoms ( cnf_prefix//sav_tag, n, box, r*box ) ! Save configuration
END DO ! End loop over blocks
CALL run_end ( calc_variables() ) ! Output run averages
! Final overlap check and pressure calculation
IF ( overlap ( box ) ) THEN ! should never happen
WRITE ( unit=error_unit, fmt='(a)') 'Overlap in final configuration'
STOP 'Error in mc_npt_hs'
END IF
CALL write_cnf_atoms ( cnf_prefix//out_tag, n, box, r*box ) ! Write out final configuration
CALL deallocate_arrays
CALL conclusion
CONTAINS
FUNCTION calc_variables ( ) RESULT ( variables )
USE averages_module, ONLY : variable_type
IMPLICIT NONE
TYPE(variable_type), DIMENSION(3) :: variables ! The 3 variables listed below
! This routine calculates all variables of interest and (optionally) writes them out
! They are collected together in the variables array, for use in the main program
TYPE(variable_type) :: m_r, v_r, density
REAL :: vol, rho
! Preliminary calculations (m_ratio, v_ratio, box etc already known)
vol = box**3 ! Volume
rho = REAL(n) / vol ! Density
! Variables of interest, of type variable_type, containing three components:
! %val: the instantaneous value
! %nam: used for headings
! %method: indicating averaging method
! If not set below, %method adopts its default value of avg
! The %nam and some other components need only be defined once, at the start of the program,
! but for clarity and readability we assign all the values together below
! Move acceptance ratios
m_r = variable_type ( nam = 'Move ratio', val = m_ratio, instant = .FALSE. )
v_r = variable_type ( nam = 'Volume ratio', val = v_ratio, instant = .FALSE. )
! Density
density = variable_type ( nam = 'Density', val = rho )
! Collect together for averaging
variables = [ m_r, v_r, density ]
END FUNCTION calc_variables
END PROGRAM mc_npt_hs