g_energy


Main Table of Contents

VERSION 3.0
Tue 24 Jul 2001


Description

g_energy extracts energy components or distance restraint data from an energy file. The user is prompted to interactively select the energy terms she wants.

When the -viol option is set, the time averaged violations are plotted and the running time-averaged and instantaneous sum of violations are recalculated. Additionally running time-averaged and instantaneous distances between selected pairs can be plotted with the -pairs option.

Average and RMSD are calculated with full precision from the simulation (see printed manual). Drift is calculated by performing a LSQ fit of the data to a straight line. Total drift is drift multiplied by total time.

With -fee a free energy estimate is calculated using the formula: G = -ln < e ^ (E/kT) > * kT, where k is Boltzmann's constant, T is set by -fetemp and the average is over the ensemble (or time in a trajectory). Note that this is in principle only correct when averaging over the whole (Boltzmann) ensemble and using the potential energy. This also allows for an entropy estimate using G = H - T S, where H is the enthalpy (H = U + p V) and S entropy.

When a second energy file is specified (-f2), a free energy difference is calculated dF = -kT ln < e ^ -(EB-EA)/kT >A , where EA and EB are the energies from the first and second energy files, and the average is over the ensemble A. NOTE that the energies must both be calculated from the same trajectory.

Files

optionfilenametypedescription
-f ener.edr Input Generic energy: edr ene
-f2 ener.edr Input, Opt. Generic energy: edr ene
-s topol.tpr Input, Opt. Generic run input: tpr tpb tpa
-o energy.xvg Output xvgr/xmgr file
-viol violaver.xvg Output, Opt. xvgr/xmgr file
-pairs pairs.xvg Output, Opt. xvgr/xmgr file
-corr enecorr.xvg Output, Opt. xvgr/xmgr file
-vis visco.xvg Output, Opt. xvgr/xmgr file
-ravg runavgdf.xvg Output, Opt. xvgr/xmgr file

Other options

optiontypedefaultdescription
-[no]h bool no Print help info and quit
-[no]X bool no Use dialog box GUI to edit command line options
-nice int 19 Set the nicelevel
-b time -1 First frame (ps) to read from trajectory
-e time -1 Last frame (ps) to read from trajectory
-[no]w bool no View output xvg, xpm, eps and pdb files
-[no]fee bool no Do a free energy estimate
-fetemp real 300 Reference temperature for free energy calculation
-zero real 0 Subtract a zero-point energy
-[no]sum bool no Sum the energy terms selected rather than display them all
-[no]dp bool no Print energies in high precision
-[no]mutot bool no Compute the total dipole moment from the components
-skip int 0 Skip number of frames between data points
-[no]aver bool no Print also the X1,t and sigma1,t, only if only 1 energy is requested
-nmol int 1 Number of molecules in your sample: the energies are divided by this number
-ndf int 3 Number of degrees of freedom per molecule. Necessary for calculating the heat capacity
-[no]fluc bool no Calculate autocorrelation of energy fluctuations rather than energy itself
-acflen int -1 Length of the ACF, default is half the number of frames
-[no]normalize bool yes Normalize ACF
-P enum 0 Order of Legendre polynomial for ACF (0 indicates none): 0, 1, 2 or 3
-fitfn enum none Fit function: none, exp, aexp, exp_exp or vac
-ncskip int 0 Skip N points in the output file of correlation functions
-beginfit real 0 Time where to begin the exponential fit of the correlation function
-endfit real -1 Time where to end the exponential fit of the correlation function, -1 is till the end


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