Rst-wham-2d

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RST Utilities

• rst-samples
• rst-wham
• rst-wham-2d

Name

rst-wham-2d

Synopsis

rst-wham-2d

Px[=0|pi|val]hist_min_x hist_max_x num_bins_x

Py[=0|pi|val]hist_min_y hist_max_y num_bins_y

tol temperature numpad metadatafile freefile usemask

Description

These programs (wham and wham-2d) implement the Weighted Histogram Analysis Method of Kumar, et al ("Multidimensional free-energy calculations using the weighted histogram analysis method", J. Comput. Chem., 16:1339-1350, 1995). The code generally follows the notation used by Benoit Roux ("The calculation of the potential of mean force using computer simulations", Comput. Phys. Comm., 91:275-282, 1995). Consult these papers for the theoretical background and justification for the method.

Arguments

The command line arguments largely have the same meaning as they do for the one dimensional rst-wham program.

Px (Py) The periodicity arguments are not optional. "Px" by itself indicates that the first dimension of the reaction coordinate has a period of 360. "Px=0" turns off periodicity. "Px=pi" specifies a period of 2*pi, and "Px=val" allows you to choose an arbitrary value for the period.

hist_min_x hist_max_x num_bins_x behave exactly like hist_min, hist_max, and num_bins do in the 1 dimensional program. Py, hist_min_y, etc., behave the same as Px, hist_min_x, etc., except they control the second coordinate of the PMF.

use_mask expects an integer value, and if its values is non-zero turns on the automasking feature, which causes bins for which there is no sample data to be excluded from the wham calculation.

File formats

metadata As with regular 1 dimensional wham, each line of the metadata file should either be blank, begin with a "#", or have the following format /path/to/timeseries/file loc_win_x loc_win_y spring_x spring_y [correl time] [temp] This first field is the name of one of the time series files. loc_win_x and loc_win_y are the locations of the minimum of the biasing terms in the first and second dimensions of the reaction coordinate. spring_x and spring_y are the spring constants used for the biasing potential in this simulation, assuming the biasing potential is of the format $V= \frac{1}{2}(k_x (x-x_0)^2 + k_y(y-y_0)^2 )$ The sixth argument ("correl time") specifies the decorrelation time for your time series, in units of time steps. It is only used when generating fake data sets for Monte Carlo bootstrap error analysis, where it modulates the number of points per fake data set. This argument is optional, and is ignored if you don't do error analysis. If you're doing multiple temperatures but not bootstrapping, set it to any integer value as a placeholder, and it'll be ignored. See section for more discussion about how to do bootstrapping. Finally, the last field is the temperature this simulation was run at. If not supplied, the temperature specified on the command line is used. In the present version of the code, you must either leave the temperature unspecified for all simulations or specify it for all simulations. The time series files must follow one of two formats, depending on whether the temperature was specified in the metadata file. If no temperature was specified, the file should contain three columns, where the first is the time (which isn't actually used), and the second and third are the position of the system along the x and y reaction coordinates, respectively. Both numbers should be in floating point format. Lines beginning with "#" are ignored as comments. Additional columns of data are ignored. If the simulation temperature is specified, there must be a fourth column of data, containing the system's potential energy at that time point. It should be a floating point value. See the section on replica exchange for more details.

freefile The output largely resembles that for wham, except with more columns. The first line echoes the command line, followed by a specification of the periodicity, and the number of windows. The iteration lines have the same meaning. When the current value for the PMF is dumped, the format looks like -172.500000 -172.500000 1.968750 15.394489 -172.500000 -157.500000 2.574512 5.522757 -172.500000 -142.500000 3.147538 2.094142 -172.500000 -127.500000 3.505869 1.141952 where the first two columns are the values of the first and second dimensions of the reaction coordinate, the third column is the PMF, and the last column is the unnormalized probability. Once the calculation has converged, wham will produce output resembling # Dumping simulation biases, in the metadata file order # Window F (free energy units) #0 -0.000004 #1 -0.156869 #2 -0.534845 #3 -2.445469 These are the final F values from the wham calculation, and can be used for computing weighted averages for properties other than the free energy. If you specified a nonzero number of Monte Carlo bootstrap error analysis trials, you will see lines that resemble #MC trial 0: 990 iterations #MC trial 1: 973 iterations #MC trial 2: 970 iterations #MC trial 3: 981 iterations #MC trial 4: 984 iterations at the end of the file. The free energy data file is written when the calculation converges, and resembles: -232.500000 -232.500000 4.812986 0.003185 0.000001 0.000000 -232.500000 -217.500000 4.830312 0.003741 0.000001 0.000000 -232.500000 -202.500000 4.898622 0.001009 0.000000 0.000000 The first two columns are the locations along the first and second dimensions of the reaction coordinate. The third is the free energy, while the fourth is the statistical uncertainty in the free energy. The fifth and sixth columns are the normalized probability and its statistical uncertainty. The two uncertainty columns will be zero if you did not use Monte Carlo bootstrapping.