add the npt_qtb

Author: luowh35

doc/gpumd/input_parameters/ensemble_standard.rst

@@ -59,6 +59,17 @@ Optional key-value parameters can be appended in any order::
 - :attr:`N_f`: number of frequency grid points used in the filter construction (default: ``100``)
 - :attr:`seed`: random seed (default: ``880302``)
 
+:attr:`npt_qtb`
+^^^^^^^^^^^^^^^
+If the first parameter is :attr:`npt_qtb`, it combines the :term:`QTB` thermostat with a Berendsen barostat for NPT simulations with nuclear quantum effects.
+This is equivalent to using ``fix nph`` + ``fix qtb`` in LAMMPS.
+The format is::
+
+  ensemble npt_qtb <T_1> <T_2> <T_coup> {<pressure_control_parameters>} [f_max <f_max>] [N_f <N_f>] [seed <seed>]
+
+The pressure control parameters are identical to those of :attr:`npt_ber` (isotropic, orthogonal, or triclinic).
+The optional QTB key-value parameters (:attr:`f_max`, :attr:`N_f`, :attr:`seed`) can be appended after the pressure coupling constant.
+
 :attr:`npt_ber`
 ^^^^^^^^^^^^^^^
 If the first parameter is :attr:`npt_ber`, it means that the ensemble for the current run is NPT (isothermal–isobaric) generated by using the :ref:`Berendsen barostat <berendsen_barostat>`.