change_box

This keyword is used to change the simulation box. The box variables and the atom positions are changed according to the following equations:

\[\begin{split}\left( \begin{array}{ccc} a_x^{\rm new} & b_x^{\rm new} & c_x^{\rm new} \\ a_y^{\rm new} & b_y^{\rm new} & c_y^{\rm new} \\ a_z^{\rm new} & b_z^{\rm new} & c_z^{\rm new} \end{array} \right) = \left( \begin{array}{ccc} \mu_{xx} & \mu_{xy} & \mu_{xz} \\ \mu_{yx} & \mu_{yy} & \mu_{yz} \\ \mu_{zx} & \mu_{zy} & \mu_{zz} \\ \end{array} \right) \left( \begin{array}{ccc} a_x^{\rm old} & b_x^{\rm old} & c_x^{\rm old} \\ a_y^{\rm old} & b_y^{\rm old} & c_y^{\rm old} \\ a_z^{\rm old} & b_z^{\rm old} & c_z^{\rm old} \end{array} \right); \\ \left( \begin{array}{c} x^{\rm new}_i \\ y^{\rm new}_i \\ z^{\rm new}_i \end{array} \right) = \left( \begin{array}{ccc} \mu_{xx} & \mu_{xy} & \mu_{xz} \\ \mu_{yx} & \mu_{yy} & \mu_{yz} \\ \mu_{zx} & \mu_{zy} & \mu_{zz} \\ \end{array} \right) \left( \begin{array}{c} x_i^{\rm old} \\ y_i^{\rm old} \\ z_i^{\rm old} \end{array} \right).\end{split}\]

The deformation matrix \(\mu_{\alpha\beta}\) will be specified by the parameters of this keyword, as we detail below.

Syntax

This keyword accepts 1 or 3 or 6 parameters.

In the case of 1 parameter \(\delta\) (in units of Ångstrom):

change_box <delta>

we have

\[\begin{split}\left( \begin{array}{ccc} \mu_{xx} & \mu_{xy} & \mu_{xz} \\ \mu_{yx} & \mu_{yy} & \mu_{yz} \\ \mu_{zx} & \mu_{zy} & \mu_{zz} \\ \end{array} \right) = \left( \begin{array}{ccc} \frac{a_x^{\rm old} + \delta}{a_x^{\rm old}} & 0 & 0 \\ 0 & \frac{b_y^{\rm old} + \delta}{b_y^{\rm old}} & 0 \\ 0 & 0 & \frac{c_z^{\rm old} + \delta}{c_z^{\rm old}} \\ \end{array} \right)\end{split}\]

In the case of 3 parameters, \(\delta_{xx}\) (in units of Ångstrom), \(\delta_{yy}\) (in units of Ångstrom), and \(\delta_{zz}\) (in units of Ångstrom):

change_box <delta_xx> <delta_yy> <delta_zz>

we have

\[\begin{split}\left( \begin{array}{ccc} \mu_{xx} & \mu_{xy} & \mu_{xz} \\ \mu_{yx} & \mu_{yy} & \mu_{yz} \\ \mu_{zx} & \mu_{zy} & \mu_{zz} \\ \end{array} \right) = \left( \begin{array}{ccc} \frac{a_x^{\rm old} + \delta_{xx}}{a_x^{\rm old}} & 0 & 0 \\ 0 & \frac{b_y^{\rm old} + \delta_{yy}}{b_y^{\rm old}} & 0 \\ 0 & 0 & \frac{c_z^{\rm old} + \delta_{zz}}{c_z^{\rm old}} \\ \end{array} \right)\end{split}\]

In the case of 6 parameters (the box type must be triclinic), \(\delta_{xx}\) (in units of Ångstrom), \(\delta_{yy}\) (in units of Ångstrom), \(\delta_{zz}\) (in units of Ångstrom), \(\epsilon_{yz}\) (dimensionless strain), \(\epsilon_{xz}\) (dimensionless strain), and \(\epsilon_{xy}\) (dimensionless strain):

change_box <delta_xx> <delta_yy> <delta_zz> <epsilon_yz> <epsilon_xz> <epsilon_xy>

we have

\[\begin{split}\left( \begin{array}{ccc} \mu_{xx} & \mu_{xy} & \mu_{xz} \\ \mu_{yx} & \mu_{yy} & \mu_{yz} \\ \mu_{zx} & \mu_{zy} & \mu_{zz} \\ \end{array} \right) = \left( \begin{array}{ccc} \frac{a_x^{\rm old} + \delta_{xx}}{a_x^{\rm old}} & \epsilon_{xy} & \epsilon_{xz} \\ \epsilon_{yx} & \frac{b_y^{\rm old} + \delta_{yy}}{b_y^{\rm old}} & \epsilon_{yz} \\ \epsilon_{zx} & \epsilon_{zy} & \frac{c_z^{\rm old} + \delta_{zz}}{c_z^{\rm old}} \\ \end{array} \right)\end{split}\]