# F opt

The `f_opt`

keyword determines whether a "self-consistent sigma" calculation is performed to optimize the effective **translational** hard-sphere diameters of the different components (`f_opt = .true.`

, which is also the default) as presented in Ref. ^{[1]}, or instead the simpler treatment of Lai et al.^{[2]}, which follows the monocomponent formalism, is used (`f_opt = .false.`

). For the effective *rotational* hard-sphere diameters, see `f_rot_opt`

.

## Monocomponent hard-sphere diameter

In the original 2PT paper by Lin et al.^{[3]}, the effective hard-sphere diameter of a monocomponent system (all molecules/groups are the same) is not explicitly calculated. Instead, the fluidicity is uniquely defined from the thermodynamic state of the system, [math](N,V,T)[/math], and the (translational) zero-frequency density of states, [math]S_\text{trn}(0)[/math].

## References

- ↑
M.A. Caro, T. Laurila, and O. Lopez-Acevedo.
*Accurate schemes for calculation of thermodynamic properties of liquid mixtures from molecular dynamics simulations*. J. Chem. Phys.**145**, 244504 (2016). - ↑
P.-K. Lai, C.-M. Hsieh and S.-T. Lin.
*Rapid determination of entropy and free energy of mixtures from molecular dynamics simulations with the two-phase thermodynamic model*. Phys. Chem. Chem. Phys.**14**, 15206 (2012). - ↑
S.-T. Lin, M. Blanco and W.A. Goddard III.
*The two-phase model for calculating thermodynamic properties of liquids from molecular dynamics: Validation for the phase diagram of Lennard-Jones fluids*. J. Chem. Phys.**119**, 11792 (2003).