4.13 WHAT='MUR_LC'

With this option the code runs several self-consistent calculations at different geometries. The runs can be done in parallel when several images are available. This option has two working modes controlled by the logical variable lmurn. When lmurn=.TRUE. the total energy as a function of the volume is interpolated by a Murnaghan equation and a plot of the energy as a function of the volume and of the pressure as a function of the volume is produced. The volume is changed by changing only celldm(1). celldm(2)...celldm(6) remain fixed at the values given as input of pw.x. When lmurn=.FALSE. the energy is calculated in a uniform grid of parameters composed of ngeo(1) x ngeo(2)... x ngeo(6) points. The energies are fitted with a quadratic or quartic polynomial of N_k variables, where N_k is the number of independent crystal parameters for the given crystal system. A plot of the energy as a function of the lattice constant is produced for cubic systems. For solids of the hexagonal, tetragonal, and trigonal systems contour plots of the energy as a function of the two crystal parameters (a and c/a or a and cos$\alpha$ ) are plotted. For orthorhombic systems contour plots of the energy as a function of a and b/a are plotted for each value of c/a . Presently no graphical tool is implemented to plot the energy for monoclinic and triclinic crystal systems. When lmurn=.FALSE. the bulk modulus is not calculated. To obtain it, you can calculate the elastic constants at the minimum geometry (see the option what='mur_lc_elastic_constants'). With this option the pressure control is active. You can specify a finite pressure and the enthalpy is minimized instead of the energy. Note however that if the minimum is distant from the starting configuration its associated error can be large, larger for the quadratic than for the Murnaghan interpolation. For this reason the present option should be used starting from the minimum found by pw.x using the vc-relax option and the pressure should not be too different from the pressure used for vc-relax. Note that with this option the atomic coordinates are relaxed at each geometry even if you specified calculation='scf' in the pw.x input. Use frozen_ion=.TRUE. if you want to keep them fixed. To increase the maximum number of ionic iterations use calculation='relax' and give nstep (otherwise the default is 20 ). Only the bfgs relaxation is supported by this option. When lel_free_energy=.TRUE. the code makes also an electronic bands dos calculation at each geometry, computes the electronic thermodynamic quantities as a function of temperature and writes them in separate files. These files can be used to add the electronic contribution to the anharmonic properties with the option mur_lc_t.
This option can be controlled by the following variables:

ngeo(1),...,ngeo(6) : the number of geometries to use for each 
             celldm parameter. The lattice constant of these 
             geometries is calculated from the input of pw.x. 
             celldm(1),...,celldm(6) of this input is used 
             for the central geometry. For the others celldm(1),
             ...,celldm(6), are changed in steps of step_ngeo(1),
             ...,step_ngeo(6). ngeo(1) must be odd. Only the 
             values of celldm relevant for each Bravais lattice 
             are actually changed.
             Default: integer 1,1,1,1,1,1 for what=scf_*, 
             9,1,1,1,1,1 for what=mur_lc_* and lmurn=.TRUE. or 
             for cubic systems, 5 on all the relevant celldm 
             parameters when lmurn=.FALSE. and the system
             is not cubic.
step_ngeo(1),...,step_ngeo(6) : The step between the lattice 
             constants at different geometries. step_ngeo(1) is, 
             in atomic units, the change of a, step_ngeo(2), 
             step_ngeo(3) are dimensionless and are the changes 
             of the ratios b/a, c/a, step_ngeo(4), step_ngeo(5), &
             step_ngeo(6) are the changes in degree of the 
             angles alpha, beta, and gamma. The cosine of the 
             angle is calculated by the program.
             Default: real 0.05 a.u., 0.02, 0.02, 0.5, 0.5, 0.5
lmurn       : if .TRUE. the Murnaghan fit is done. Only ngeo(1) 
             values of the energy are fitted, the other values 
             of ngeo are not used. if .FALSE. use a quadratic 
             or quartic function to interpolate the energy as 
             a function of all celldm parameters. The number of 
             self-consistent calculations is ngeo(1) x ngeo(2) 
             x ngeo(3) x ngeo(4) x ngeo(5) x ngeo(6). In this 
             case only the minimum energy and the optimal celldm 
             are given in output. 
             Default: .TRUE. 
show_fit   : if .TRUE. show the contour plot of the fitted 
             energy instead of the energy. Used by default 
             when reduced_grid is .TRUE.
             Default: logical .FALSE.
frozen_ions: if .TRUE. the atomic coordinates are obtained by 
             straining the coordinates given in the pw.x input 
             to the new cell parameters (equivalent to keep the 
             crystal coordinates fixed) and kept fixed. If .FALSE. 
             the atomic coordinates are relaxed at each geometry.
             Default: logical .FALSE.
vmin_input : minimum volume for the plot of the energy as a 
             function of volume.
             Default: real 0.98 times the volume of the first 
             geometry.
vmax_input : maximum volume for the plot of the energy as a 
             function of volume.
             Default: real 1.02 times the volume of the last 
             geometry.
deltav     : distance between two volumes in the plot of the 
             energy as a function of the volume.
             Default: real calculated from nvol.
nvol       : number of volumes in Murnaghan plot.
             Default : integer 51
lquartic   : if .TRUE. fit the energy with a quartic polynomial.
             Default : logical .TRUE.
lsolve     : choose the algorithm used to fit the quartic 
             polynomial parameters.
             Allowed values:
             1 explicitly minimize chi^2 (usually less accurate 
             than the other two. Should be used only for tests).
             2 Use the QR algorithm to minimize chi^2 (lapack 
             routine dgels) 3 Use the SVD algorithm to minimize 
             chi^2 (lapack routine dgelss).
             Default: integer 2
flevdat    : file where the Murnaghan equation is written. The 
             results of the Murnaghan fit are then written in 
             flevdat.ev.out.
             Default: character(len=*) 'output_ev.dat'
flpsmur    : postscript file of the Murnaghan plot.
             Default: character(len=*) 'output_mur'
lel_free_energy : if .TRUE. computes the electronic thermodynamic 
             properties (energy, free energy, entropy, and constant 
             strain heat capacity) at each temperature and plots 
             them. See the scf_dos option for the parameters that 
             control the calculation.
             Default: .FALSE.
ncontours  : the number of contours in the energy plot. These 
             levels can be determined automatically by the code 
             or defined by the user. The energy levels can be 
             defined after the INPUT_THERMO namelist but before 
             the path, as a list:
             energy_level(1)      color(1)
             ...
             energy_level(ncontours)   color(ncontours) 
             Color is a string of the type color_red, color_green, 
             etc.
             The list of available colors is at the beginning of 
             each gnuplot script. energy_level is in Ry units.
             Default: integer 9
do_scf_relax : if .TRUE. the code makes a self-consistent relax 
             calculation at the equilibrium geometry to find 
             the optimized atomic coordinates. This step is 
             needed only for solids that have internal degrees 
             of freedom in the unstrained configuration. 
             If .FALSE. the coordinates of the input geometry 
             are strained uniformly to the equilibrium geometry.
             Default: logical .FALSE. 
flenergy   : name of the file that contains the energy in a 
             form that can be used by gnuplot to make contour 
             plots.
             Defaults: character(len=*) 'output_energy'
flpsenergy : file with the contour plots of the energy as a 
             function of the crystal parameters.
             Default: character(len=*) 'output_energy'

An example for this option can be found in example05.
Number of tasks for this option:
ngeo(1) when lmurn=.TRUE.,
ngeo(1)x ngeo(2)x ngeo(3)x ngeo(4)x ngeo(5)x ngeo(6) when lmurn=.FALSE..