External Field

The presence of an external field is flagged by the extern directive. The next line in the FIELD file should have another directive indicating what type of field is to be applied. On the following lines comes the mxfld parameters, five per line, that describe the field. In the include files supplied with DL_POLY_2 mxfld is set to 10.

The variables pertaining to each potential are described in table 4.15.

Table 4.15: External fields

key	potential type	Variables (1-4)				functional form
elec	Electric field	$E_x$	$E_y$	$E_z$		$\mbox{$\underline{F}$} = q.\mbox{$\underline{E}$}$
oshm	Oscillating Shear	$A$	$n$			$\mbox{$\underline{F}$}_x = A cos (2 n\pi. z/L_z)$
shrx	Continuous Shear	$A$	$z_0$			$\mid z \mid > z_0$: $\mbox{$\underline{v}$}_x = (1/2)A(\mid z \mid / z)$
grav	Gravitational Field	$G_x$	$G_y$	$G_z$		$\mbox{$\underline{F}$} = m.\mbox{$\underline{G}$}$
magn	Magnetic Field	$H_x$	$H_y$	$H_z$		$\mbox{$\underline{F}$} = q(\mbox{$\underline{v}$}\times\mbox{$\underline{H}$})$
sphr	Containing Sphere	$A$	$R_0$	$n$	$R_{\rm cut}$	$r > R_{\rm cut}$: $\mbox{$\underline{F}$} = A(R_0 - r)^{-n}$