[lammps-users] fix_rdf output

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1

Dear all,

Could you let me know what each column mean in rdf output?
Followings are my situation:

I used such commands:
fix 1 all rdf 10000 rdf.out 100 1 1

and, this is a part of the output:
# Timestep 10000
r, g(1,1,r), ncoord(1,1,r)
0.027775 0.000000 0.000000
0.083325 0.000000 0.000000
0.138875 0.000000 0.000000
0.194424 0.000000 0.000000
0.249974 0.000000 0.000000
0.305524 0.000000 0.000000
0.361074 0.000000 0.000000
0.416624 0.000000 0.000000
0.472173 0.000000 0.000000
0.527723 0.000000 0.000000
0.583273 0.000000 0.000000
0.638823 0.000000 0.000000
0.694373 0.000000 0.000000
0.749923 0.000000 0.000000
0.805472 0.000000 0.000000
0.861022 0.000000 0.000000
0.916572 0.000000 0.000000
0.972122 0.000000 0.000000
1.027672 0.000000 0.000000
1.083221 0.000000 0.000000
1.138771 0.000000 0.000000
1.194321 0.000000 0.000000
1.249871 0.000000 0.000000
1.305421 0.000000 0.000000
1.360971 0.000000 0.000000
1.416520 0.000000 0.000000
1.472070 0.000000 0.000000
1.527620 0.000000 0.000000
1.583170 0.000000 0.000000
1.638720 0.000000 0.000000
1.694270 0.000000 0.000000
1.749819 0.000000 0.000000
1.805369 0.000000 0.000000
1.860919 0.000000 0.000000
1.916469 0.000000 0.000000
1.972019 0.000000 0.000000
2.027568 0.000000 0.000000
2.083118 0.000000 0.000000
2.138668 0.000000 0.000000
2.194218 0.110680 0.005249
2.249768 1.579229 0.083990
2.305318 6.216708 0.409449
2.360867 18.834509 1.443570
2.416417 31.394009 3.249344
2.471967 40.986944 5.716535
2.527517 30.613414 7.643045
2.583067 18.289373 8.845144
2.638616 8.189672 9.406824
2.694166 3.670770 9.669291
2.749716 1.409583 9.774278
2.805266 0.609441 9.821522
2.860816 0.000000 9.821522
2.916366 0.062655 9.826772
2.971915 0.000000 9.826772
3.027465 0.116282 9.837270
3.083015 0.056065 9.842520
3.138565 0.216390 9.863517
3.194115 0.208929 9.884514
3.249664 0.807391 9.968504
3.305214 1.365840 10.115486
3.360764 3.491380 10.503937
4.416211 0.000000 30.614173
4.471761 0.000000 30.614173
4.527310 0.000000 30.614173
4.582860 0.000000 30.614173
4.638410 0.000000 30.614173
4.693960 0.000000 30.614173
4.749510 0.000000 30.614173
4.805059 0.000000 30.614173
4.860609 0.000000 30.614173
4.916159 0.000000 30.614173
4.971709 31.692224 38.330709
5.027259 0.000000 38.330709
5.082809 0.000000 38.330709
5.138358 0.000000 38.330709
5.193908 0.000000 38.330709
5.249458 0.000000 38.330709
5.305008 0.000000 38.330709
5.360558 0.000000 38.330709
5.416107 0.000000 38.330709
5.471657 0.000000 38.330709
5.527207 0.000000 38.330709

The 2nd column looks like g(r) but it converges into 1, so one needs
normalization factor.

I want to know what 2nd and 3rd column indicate.
Then, I can find the normalization factor.

Best regards,

Minwoong

2

Minwoong,

The second column is the radial distribution function (RDF), also known as g(r). The third column is the coordination number.

Your data looks quite interesting. Your values for g(r) don't seem to converge to unity within the distance you show. Apparently you must be simulating a structured fluid or a solid of some sort.

See: http://lammps.sandia.gov/doc/fix_rdf.html

Also, you might try looking at the fix_rdf source code. It is quite simple and might help you see what the calculation is doing.

Paul