<div>Dear Gromacs Users</div>
<div> </div>
<div>I am confused about definition of improper dihedral angle in charmm27, which is compared to oplsaa.</div>
<div> </div>
<div>Why charmm ff in gromacs give <strong>double</strong> items for the same dihedral angle.</div>
<div>e.g.  for charmm27 ASN</div>
<div>        CG      ND2     CB      OD1<br>       <font color="#ff0000"> CG      CB      ND2     OD1<br></font>        ND2     CG      HD21    HD22<br>        <font color="#ff0000">ND2     CG      HD22    HD21<br></font><font style="BACKGROUND-COLOR:#ffffff" color="#000000">in opls aa for ASN</font></div>

<div>    CG    CB    CA     C     dih_ASN_chi1_C_C_C_CO<br>    CA    CB    CG   ND2     dih_ASN_chi2_C_C_CO_N<br></div>
<div>Thanks for advance!</div>
<div> </div>
<div>Tom</div>
<div> </div>
<div>PS:</div>
<div> </div>
<div>the detail is as follows </div>
<div> </div>
<div>------------------------------------------------</div>
<div><strong>in charmm27.ff/aminoacids.rtp</strong></div>
<div>[ ASN ]<br> [ atoms ]<br>        N       NH1     -0.47   0<br>        HN      H       0.31    1<br>        CA      CT1     0.07    2<br>        HA      HB      0.09    3<br>        CB      CT2     -0.18   4<br>        HB1     HA      0.09    5<br>
        HB2     HA      0.09    6<br>        CG      CC      0.55    7<br>        OD1     O       -0.55   8<br>        ND2     NH2     -0.62   9<br>        HD21    H       0.32    10<br>        HD22    H       0.30    11<br>
        C       C       0.51    12<br>        O       O       -0.51   13<br> [ bonds ]<br>        CB      CA<br>        CG      CB<br>        ND2     CG<br>        N       HN<br>        N       CA<br>        C       CA<br>
        C       +N<br>        CA      HA<br>        CB      HB1<br>        CB      HB2<br>        ND2     HD21<br>        ND2     HD22<br>        C       O<br>        CG      OD1<br> [ impropers ]<br>        N       -C      CA      HN<br>
        C       CA      +N      O<br><font color="#ff0000">        CG      ND2     CB      OD1<br>        CG      CB      ND2     OD1<br>        ND2     CG      HD21    HD22<br>        ND2     CG      HD22    HD21<br></font> [ cmap ]<br>
        -C      N       CA      C       +N</div>
<div>-------------------------------------------</div>
<div>in<strong> oplsaa.ff/aminoacids.rtp</strong></div>
<div>[ ASN ]<br> [ atoms ]<br>     N    opls_238   -0.500     0<br>     H    opls_241    0.300     0<br>    CA    opls_224B   0.140     1<br>    HA    opls_140    0.060     1<br>    CB    opls_136   -0.120     2<br>   HB1    opls_140    0.060     2<br>
   HB2    opls_140    0.060     2<br>    CG    opls_235    0.500     3<br>   OD1    opls_236   -0.500     3<br>   ND2    opls_237   -0.760     4<br>  HD21    opls_240    0.380     4<br>  HD22    opls_240    0.380     4<br>
     C    opls_235    0.500     5<br>     O    opls_236   -0.500     5<br> [ bonds ]<br>     N     H<br>     N    CA<br>    CA    HA<br>    CA    CB<br>    CA     C<br>    CB   HB1<br>    CB   HB2<br>    CB    CG<br>    CG   OD1<br>
    CG   ND2<br>   ND2  HD21<br>   ND2  HD22<br>     C     O<br>    -C     N<br> [ dihedrals ] ; override some with residue-specific ones<br>     N    CA    CB    CG     dih_ASN_chi1_N_C_C_C<br>    CG    CB    CA     C     dih_ASN_chi1_C_C_C_CO<br>
    CA    CB    CG   ND2     dih_ASN_chi2_C_C_CO_N<br></div>