External Fields

In addition to the molecular force field, DL_POLY_2 allows the use of an external force field. Examples of field available include:

1. Electric field: (elec)
   

   $$\mbox{$\underline{F_i}$} = \mbox{$\underline{F_i}$} + q_i. \mbox{$\underline{H}$}$$ (2.107)

   
   

2. Oscillating shear: (oshm)
   

   $$\mbox{$\underline{F}$}_{x}=A\cos(2n\pi.z/L_{z})$$ (2.108)

   
   

3. Continuous shear: (shrx)
   

   $$\mbox{$\underline{v}$}_{x}=\frac{1}{2}A\frac{\vert z\vert}{z}~~~~~~~~~~~~~:\vert z\vert>z_{0}$$ (2.109)

   
   

4. Gravitational field: (grav)
   

   $$\mbox{$\underline{F_i}$} = \mbox{$\underline{F_i}$} + m_i. \mbox{$\underline{H}$}$$ (2.110)

   
   

5. Magnetic field: (magn)
   

   $$\mbox{$\underline{F_i}$} = \mbox{$\underline{F_i}$} + q_i.(\mbox{$\underline{v_i}$}\wedge \mbox{$\underline{H}$})$$ (2.111)

   
   

6. Containing sphere: (sphr)
   

   $$\mbox{$\underline{F}$}=A(R_{0}-r)^{-n}~~~~~~~~~~~~: r>R_{cut}$$ (2.112)

   
   

7. Repulsive wall: (zbnd)
   

   $$\mbox{$\underline{F}$}=A(z_{o}-z)~~~~~~~~~~~~: z>z_{o}$$ (2.113)

   
   

It is recommended that the use of an external field should be accompanied by a thermostat (this does not apply to examples 6 and 7, since these are conservative fields). The user is advised to be careful with units!

In DL_POLY_2 external field forces are handled by the routine EXTNFLD.