Units

Internally all DL_POLY_2 subroutines and functions assume the use of the following defined molecular units:

1. The unit of time ($t_{o}$) is $1\times 10^{-12}$ seconds (i.e. picoseconds).
2. The unit of length ($\ell_{o}$) is $1\times 10^{-10}$ metres (i.e. Ångstroms).
3. The unit of mass ($m_{o}$) is $1.6605402\times 10^{-27}$ kilograms (i.e. atomic mass units).
4. The unit of charge ($q_{o}$) is $1.60217733\times 10^{-19}$ coulombs (i.e. unit of proton charge).
5. The unit of energy ( $E_{o}=m_{o}(\ell_{o}/t_{o})^{2}$) is $1.6605402\times 10^{-23}$ Joules (10 J mol$^{-1}$).
6. The unit of pressure ( ${\cal P}_{o}=E_{o}\ell_{o}^{-3}$) is $1.6605402\times 10^{7}$ Pascal ($166.05402$ bar).
7. Planck's constant ($\hbar$) which is $6.350780668\times E_{o}t_{o}$.

In addition the following conversion factors are used:

The coulombic conversion factor ($\gamma_{o}$) is:

$$\gamma_{o}=\frac{1}{E_{o}} \left [ \frac{q_{o}^{2}}{4\pi\epsilon_{o}\ell_{o}}\right ]= 138935.4835$$

such that:

$$U_{MKS}=E_{o}\gamma_{o}U_{Internal}$$

Where $U$ represents the configuration energy.

The Boltzmann factor ($k_{B}$) is $0.831451115~E_{o}K^{-1}$, such that:

$$T=E_{kin}/k_{B}$$

represents the conversion from kinetic energy (in internal units) to temperature (in Kelvin).

Note: In the DL_POLY_2 OUTPUT file, the print out of pressure is in units of kbars at all times. The unit of energy is either DL_POLY_2 units specified above, or in other units specified by the user at run time. The default is DL_POLY units.