ML LHEAT

ML_FF_LHEAT_MB = [logical]
Default: ML_FF_LHEAT_MB = .FALSE.

Description: This flag specifies whether the heat flux is calculated or not in the machine learning force field method.

The heat flux within machine learning force fields can is decomposed into atomic contributions written as

${\displaystyle \mathbf{q}(t) = \sum\limits_{i=1}^{N_{a}} \frac{d}{dt} \left( \mathbf{r}_{i} E_{i} \right), }$

${\displaystyle E_{i}=\frac{m_{i} \left|\mathbf{v}_{i} \right|^{2}}{2} + U_{i} }$

where $\mathbf{r}_{i}$ , $\mathbf{v}_{i}$ and $E_{i}$ denote the position vector, velocity and energy of atom $i$ , respectively. The heat flux can be further rewritten as

${\displaystyle \mathbf{q}(t) = \sum\limits_{i=1}^{N_{a}} \mathbf{v}_{i} E_{i} + \sum\limits_{i=1}^{N_{a}} \mathbf{r}_{i} \left( m_{i} \mathbf{v}_{i} \cdot \frac{d\mathbf{v}_{i}}{dt} + \sum\limits_{j=1}^{N_{a}} \mathbf{v}_{j} \cdot \nabla_{j} U_{i} \right). }$

The thermal conductivity at temperature $T$ in the Green-Kubo formalism is calculated from the correlation of the heat flux $\mathbf{q}$ as

${\displaystyle \kappa = \frac{1}{3Vk_{b}T^{2}} \int\limits_{0}^{\infty} \langle \mathbf{q}(t) \cdot \mathbf{q}(0) \rangle dt, }$

where $V$ and $k_{b}$ denotes the volume of the system and the Boltzmann constant, respectively.

The heat flux is written to the file ML_HEAT.

Related Tags and Sections

ML_FF_LMLFF, ML_FF_LEATOM_MB

Examples that use this tag