GROMACS version: 2018

GROMACS modification: No

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Hi everyone,

Recently, I am confused by the result of integration of g®. In the manul, the definition of g®_AB is g®_AB = pho®/ pho_local, the r_max for pho_local is the half of box.

Based on the definition, the integration from zero to rmax of g®_AB*pho_local will be the number of B (smaller than total number of B) in the sphere with radius r_max.

However, when I calculated the integration, I found that the result is bigger than the total number of B.

For example, if there are 26 A monomers and 26 B monomers in the system, the integration of g_AB*pho_local will smaller than 26. But I got the value larger than 46.
The pho_local = average_number/(4.0/3*pi

*rmax*rmax*rmax), here average_number is accumulate number of B at distance rmax got from the output file using gmx rdf -cn

## the integration script i used:

```
double dr = rr[1]-rr[0];
sumb = 0;
double psv = 0.0,rri;
for(i = 0; i < ri; i ++){
rri = (i + 0.5) * dr;
double sv = (4.0 / 3.0) * PI * rri * rri * rri;
double dsv = sv-psv;
sumb += (gr[i])*(dsv);
psv = sv;
cout<<"sumb = "<<sumb<<endl;
}
double pho_local = 24.8/((4.0 / 3.0) * PI * rri * rri * rri);
cout<<"total monomer number ~: "<<sumb*pho_local<<endl;;
```

I do not find anything wrong in my script. So could anyone help me to explain why the result is unexpected. Is there some misunderstanding of the definition of g® that GROMACS used to analyze data?

Thanks in advance

Best

isimuly