Dear Justin Based on your answer (You don't want to be adding 2 HZ here, just one since it is a peptide bond.), I modified LYS2 in aminoacids.hdb file
LYS2 2 1 1 H N -C CA 1 4 HZ NZ CE CD But, after pdb2gmx, I encountered with WARNING: atom HZ1 is missing in residue LYS 540 in the pdb file You might need to add atom HZ1 to the hydrogen database of building block LYS2 in the file aminoacids.hdb (see the manual) WARNING: atom HZ2 is missing in residue LYS 540 in the pdb file You might need to add atom HZ2 to the hydrogen database of building block LYS2 in the file aminoacids.hdb (see the manual). What is the reason of this issue? Is there problem in my rtp file (about LYS2 and GLU2 entries)? [ GLU2 ] [ atoms ] N N -0.28000 0 H H 0.28000 0 CA CH1 0.00000 1 CB CH2 0.00000 1 CG CH2 0.00000 1 CD C 0.380 2 OE1 OM -0.380 2 OE2 OM 0.00000 2 C C 0.380 3 O O -0.380 3 [ bonds ] N H gb_2 N CA gb_20 CA C gb_26 C O gb_4 C +N gb_9 CA CB gb_26 CB CG gb_26 CG CD gb_26 CD OE1 gb_5 CD OE2 gb_5 [ angles ] ; ai aj ak gromos type -C N H ga_31 H N CA ga_17 -C N CA ga_30 N CA C ga_12 CA C +N ga_18 CA C O ga_29 O C +N ga_32 N CA CB ga_12 C CA CB ga_12 CA CB CG ga_14 CB CG CD ga_14 CG CD OE1 ga_21 CG CD OE2 ga_21 OE1 CD OE2 ga_37 [ impropers ] ; ai aj ak al gromos type N -C CA H gi_1 C CA +N O gi_1 CA N C CB gi_2 CD OE1 OE2 CG gi_1 [ dihedrals ] ; ai aj ak al gromos type -CA -C N CA gd_4 -C N CA C gd_19 N CA C +N gd_20 N CA CB CG gd_17 CA CB CG CD gd_17 CB CG CD OE2 gd_2 [ LYS2 ] [ atoms ] N N -0.28000 0 H H 0.28000 0 CA CH1 0.00000 1 CB CH2 0.00000 1 CG CH2 0.00000 2 CD CH2 0.00000 2 CE CH2 0.00000 2 NZ NT -0.28000 3 HZ1 H 0.28000 3 HZ2 H 0.00000 3 C C 0.380 4 O O -0.380 4 [ bonds ] N H gb_2 N CA gb_20 CA C gb_26 C O gb_4 C +N gb_9 CA CB gb_26 CB CG gb_26 CG CD gb_26 CD CE gb_26 CE NZ gb_20 NZ HZ1 gb_2 NZ HZ2 gb_2 [ angles ] ; ai aj ak gromos type -C N H ga_31 H N CA ga_17 -C N CA ga_30 N CA C ga_12 CA C +N ga_18 CA C O ga_29 O C +N ga_32 N CA CB ga_12 C CA CB ga_12 CA CB CG ga_14 CB CG CD ga_14 CG CD CE ga_14 CD CE NZ ga_14 CE NZ HZ1 ga_10 CE NZ HZ2 ga_10 HZ1 NZ HZ2 ga_9 [ impropers ] ; ai aj ak al gromos type N -C CA H gi_1 C CA +N O gi_1 CA N C CB gi_2 [ dihedrals ] ; ai aj ak al gromos type -CA -C N CA gd_4 -C N CA C gd_19 N CA C +N gd_20 N CA CB CG gd_17 CA CB CG CD gd_17 CB CG CD CE gd_17 CG CD CE NZ gd_17 CD CE NZ HZ1 gd_14 Thanks in advance. -- Gromacs Users mailing list * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists * For (un)subscribe requests visit https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or send a mail to gmx-users-requ...@gromacs.org.