Constant ph molecular dynamics using GROMACS FMM & Constant pH

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Dear Experts,

I install the gromacs that suppor the constant ph MD.

Then I do the following steps.

  1. gmx pdb2gmx -o prot.gro -ignh -ff charmm36m-lambdadyn -water tip3p -ldglu -ldhis -ldasp -ldtyr -ldlys -f output.gro

  2. gmx editconf -f prot.gro -o box.gro -box 30 30 30 -c -bt cubic

  3. gmx solvate -cs spc216.gro -cp box.gro -p topol.top -o solv.gro

  4. sed ‘s/HOH/SOL/g’ solv.gro > SOLV.gro

  5. gmx grompp -f genion.mdp -c SOLV.gro -o genion.tpr -p topol.top -maxwarn 1

  6. gmx genion -s genion.tpr -o solvions.gro -p topol.top -pname SOD -nname CLA -conc 0.15 -neutral -cphcoupled -rminprotld 2.0 -rminld 3.0 -rtolld 0.3 -nobackup

But In the step 6th I got the following error message.

umber of (3-atomic) solvent molecules: 877739

Processing topology
Replacing 4920 solute molecules in topology file (topol.top) by 2439 SOD and 2481 CLA ions, and 72 lambda dynamics counterions.
Using random seed -1082671106.
Lambda dyn counterion: Determining solvent molecules not too close to non solvent…
For the solvent search, min. dist to non-solvent: 2.00, distance to residue 2.70 - 3.30 (tolerance included)
877600 of 877739
Found 867438 suitable solvents
Lambda dyn counterion: Determining solvent molecules suitable for each residue…

The following protonable residues have 0 suitable water for counterion/buffer placement: 2 19 31 32 38 39 58


Program: gmx genion, version 2024-dev-20241209-eba91f0-unknown
Source file: src/gromacs/gmxpreprocess/genion.cpp (line 321)

Fatal error:
Some residue have no suitable solvent for buffer/counterion placement. Maybe
try a bigger box?

For more information and tips for troubleshooting, please check the GROMACS
website at Common Errors — GROMACS webpage https://www.gromacs.org documentation