FIST - Morse coulombic subtraction and Genpot Funtion units

ganta.pra... at gmail.com ganta.pra... at gmail.com
Sun Nov 19 23:38:15 CET 2017


Dear CP2K team/users,

I am trying to use FIST to do GEO_OPT of a box of water molecules. I have 
following doubts.

1) How to implement coulombic subtraction in &BONDED --> Morse potential.

In CP2K the morse potential is in the form

*K1*[(1-exp(-K2*(R-R0)))^2-1])* 

But I want to include coulombic subtraction and implement the below form. 

*K1*[(1-exp(-K2*(R-R0)))^2-1]) - D*Q1*Q2/R*

where Q1 and Q2 are charges of the atoms.

Please let me know if it is possible. 

2) What will be the units of the energy for the expression in FUNCTION for 
below case. Will it be eV or CP2K internal  units? Do we need to adjust the 
FUNCTION manually to match the CP2K internal units (atomic units) ? Please 
let me know. 

         &GENPOT                                                            
                                                            
          ATOMS OWAT OWAT                                                  
                                                            
          FUNCTION ((A/(r^12))-(B/(r^6)))                                  
                                                            
          PARAMETERS A B                                                    
                                                           
          UNITS eV*angstrom^12 eV*angstrom^6                                
                                                           
          VALUES  39344.98  42.15                                          
                                                            
          VARIABLES r                                                      
                                                            
          RCUT [angstrom] $WATERCUTOFF                                      
                                                           
        &END GENPOT     

Have a nice day.

Thanks and Regards,
Prasanth.                                                 
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