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                                     Bylaska  Forum:Admin, Forum:Mod, NWChemDeveloper, bureaucrat, sysop
                                    
                                  
 
                                 
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                 Gets Around 
                
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		                        | 3:53:01 PM PDT - Wed, Aug 17th 2011  | 
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		                        Peizhi, 
 
The documentation is a little out of date. 
The following keywords are available in the fragment blocks of AIMD/MM 
>                    'size', 
>             'index_start', 
>             'shake', 
>             'switching', 
>             'bond_spring', 
>             'angle_spring', 
>             'self_interaction', 
>             'incell', 
>             'cross_bond_spring', 
>             'bond_morse', 
>             'dihedral_spring', 
>             'dihedral', 
>             'coord_number', 
 
The input (in au)  for bond_morse, dihedral, and dihedral_spring are as follows 
 
bond_morse i1 i2 k a re  
where 
E = E + k*( 1.0d0 - dexp(-a*(r-re))) )**2 
and 
r is the distance between atoms i1 and i2 
 
 
dihedral_spring i1 i2 i3 i4 k theta0 
where 
E = E + k*(phi-theta0)**2 
and 
phi is the torsion angle spanned by atoms i1 i2 i3 and i4 
 
 
dihedral i1 i2 i3 i4 k a0 theta0 
where 
E = E + k*(1.0+cos(a0*phi-phi0)) 
 
I still haven't implemented link atoms but will probably do so in the near future. 
 
Hope that helps 
Eric
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