How to use the ff-Mg-Ca-NucleicAcids in amber14sb_OL15.ff

[Lesile-Han]

Hello, I want to use the correct Ion parameter to simulating the binding of DNA and ions by all-atom MD. However, I want to use the OL15 force fields for DNA. How should I operate?

[Lesile-Han]

Hello, sir. I just download the package. I want to add CaCl2 in my systerm by Gromacs-2019.6. However, There are some errors here. I run the command : gmx genion -s ions.tpr -o triplex_solv_ions.gro -p topol.top -pname Ca2 -pq 2 -nname CXY -neutral -conc 0.15
But I carry out the em and the error is : Ca2 in topol.top don't match the Ca in xx.gro. So I change Ca in my gro to Ca2 . But the error is as follows:
Fatal error:
Something is wrong in the coordinate formatting of file triplex_solv_ions.gro.
Note that gro is fixed format (see the manual)
For more information and tips for troubleshooting, please check the GROMACS
website at http://www.gromacs.org/Documentation/Errors

How can I solve it? Could you please give me some advice? Thank you very much.