# Histogram of Dihedral Values

Hey everyone,

I’m attempting to obtain a histogram of dihedral values. Since I only care about the value of a certain dihedral, I defined a group and then used a compute command:

group DiHe type 2 3 4 5 6 7 8 9
compute 1 DiHe dihedral/local phi

To get the histogram, I used:

fix DiHeCalc DiHe ave/histo 1000 9 1 0 360 180 c_1 file DiHe.histo

The simulation run time is only 20 ps (this is just a test run), and as far as I understand, this fix command should run the aforementioned compute command over the group 9 times, with the interval between measurements being 1000 time steps (1 ps). There are 180 histogram bins, each with a size of 2 degrees, starting at 0 and ending at 360. Upon running the simulation, however, the DiHe.histo file is created but is entirely empty. I received the following error in my output file:

ERROR: Illegal fix ave/histo command

I thought that I might have defined my group incorrectly, so I later ran the fix over all atoms and nevertheless received the same error. Can someone help me out please? If you needed to obtain the histogrammed values for a certain dihedral, would you even approach the problem this way? Any advice would be greatly appreciated,

Charles Belina
Student Researcher
Skolkovo Institute of Science and Technology

Hey everyone,

I’m attempting to obtain a histogram of dihedral values. Since I only care about the value of a certain dihedral, I defined a group and then used a compute command:

group DiHe type 2 3 4 5 6 7 8 9
compute 1 DiHe dihedral/local phi

To get the histogram, I used:

fix DiHeCalc DiHe ave/histo 1000 9 1 0 360 180 c_1 file DiHe.histo

The simulation run time is only 20 ps (this is just a test run), and as far as I understand, this fix command should run the aforementioned compute command over the group 9 times, with the interval between measurements being 1000 time steps (1 ps). There are 180 histogram bins, each with a size of 2 degrees, starting at 0 and ending at 360. Upon running the simulation, however, the DiHe.histo file is created but is entirely empty. I received the following error in my output file:

ERROR: Illegal fix ave/histo command

I thought that I might have defined my group incorrectly, so I later ran the fix over all atoms and nevertheless received the same error. Can someone help me out please? If you needed to obtain the histogrammed values for a certain dihedral, would you even approach the problem this way? Any advice would be greatly appreciated,

there are two problems:
- your Nevery, Nrepeat, Nfreq is invalid. it probably should be 1000 9