(last revised, LC, VVK & SBT: 16 June 2016)

How to use the KSDT XC free-energy implemented in the LibXC library -
L. Calderin, V.V. Karasiev, and S.B. Trickey, Univ. Florida
======================================================================

I. BACKGROUND -

This HOWTO file provides instructions for use of the KSDT LSDA XC 
free-energy functional (Karasiev, Sjostrom, Dufty, Trickey, Phys. Rev. 
Lett. 112, 076403 (2014)) as implemented in the LibXC 3.0 library. 

BEWARE: Failure to follow this procedure will result in the electron 
temperature (T) being left at 0 K (zero).  

We assume that users have the LibXC library installed and know how to 
call standard ground-state LSDA XC functionals.

In addition to the standard LibXC LSDA interface (see the LibXC manual: 
http://www.tddft.org/programs/octopus/wiki/index.php/Libxc:manual#LDA), KSDT
REQUIRES an additional call to a subroutine which sets the value 
of the electron temperature (T) in Hartree atomic units. 

II. FORTRAN implementation
==========================
FORTRAN declarations and calls in the calling program should appear 
as follows (see below regarding C code):

  USE XC_F90_TYPES
  USE XC_f90_LIB
...
  TYPE(xc_f90_pointer_t) :: x_func,c_func,ksdt_func
  TYPE(xc_f90_pointer_t) :: x_info,c_info,ksdt_info
...
   call xc_f90_func_init(ksdt_func,ksdt_info,XC_LDA_XC_KSDT,XC_UNPOLARIZED)
...
   call xc_f90_lda_xc_ksdt_set_par(ksdt_func,T) !!! This call sets up the temperature T
...
   call xc_f90_lda_exc_vxc(ksdt_func,size,rho,fxc,vxc)
...
   call xc_f90_func_end(xc_func)
... 
  
III. C code implementation -
============================
A C version of the test code (next section) also is provided. 
Please refer to that code itself to see how to do the C declarations 
and calls to KSDT in LibXC.
 
IV. How to test the KSDT subroutine -
=====================================

We also provide a test code (lxc-ksdt-test-f90.f90 file) which,
if the call to KSDT is correct, will reproduce the data in Table S1 
of the Supplemental Material for the above-cited Phys. Rev. Lett.

To use the test code, proceed as follows:

1. Install the LibXC 3.0 library in $LIBXCDIR

2. Compile the lxc-ksdt-test-f90_v6.f90 file:

ifort lxc-ksdt-test-f90_v6.f90 -I $LIBXCDIR/include -L $LIBXCDIR/lib -lxcf90 -lxc -o lxc-ksdt-test-f90_v6.x

3. Execute: 

./lxc-ksdt-test-f90_v6.x > lxc-ksdt-test-f90_v6.dat

4. Compare with the reference data in lxc-ksdt-test-f90_ref_v6.dat

--end--