Enabled writing out the bandgap to out.xml

Also in this commit: Changed the Htr to eV conversion factor
according to the 2014 CODATA recommended value.

fermi/ferhis.f90

@@ -46,6 +46,8 @@ CONTAINS
     !***********************************************************************
     USE m_efnewton
     USE m_types
+    USE m_xmlOutput
+    USE m_constants
     IMPLICIT NONE
     TYPE(t_results),INTENT(INOUT)   :: results
     TYPE(t_mpi),INTENT(IN)          :: mpi
@@ -80,6 +82,7 @@ CONTAINS
 
     !     .. Local Arrays ..      
     REAL :: qc(3)
+    CHARACTER(LEN=20)    :: attributes(2)
 
     !     ..
     !***********************************************************************
@@ -119,7 +122,13 @@ CONTAINS
     efermi = results%ef
     IF (nstef.LT.n) THEN
        gap = e(INDEX(nstef+1)) - results%ef
-       IF ( mpi%irank == 0 ) WRITE (6,FMT=8050) gap
+       IF ( mpi%irank == 0 ) THEN
+          attributes = ''
+          WRITE(attributes(1),'(f20.10)'), gap*hartree_to_ev_const
+          WRITE(attributes(2),'(a)'), 'eV'
+          CALL writeXMLElement('bandgap',(/'value','units'/),attributes)
+          WRITE (6,FMT=8050) gap
+       END IF
     END IF
     IF ( mpi%irank == 0 ) THEN
        WRITE ( 6,FMT=8010) spindg* (ws-weight)

global/constants.f

@@ -8,7 +8,7 @@
       REAL,PARAMETER:: tpi_const=2.*3.1415926535897932
       REAL,PARAMETER:: fpi_const=4.*3.1415926535897932
       REAL,PARAMETER:: sfp_const=sqrt(4.*3.1415926535897932)
-      REAL,PARAMETER:: hartree_to_ev_const=27.21138505
+      REAL,PARAMETER:: hartree_to_ev_const=27.21138602 ! value from 2014 CODATA recommended values. Uncertainty is 0.00000017
       CHARACTER(2),DIMENSION(0:103),PARAMETER:: namat_const=(/
      &      'va',' H','He','Li','Be',' B',' C',' N',' O',' F','Ne',         
      &     'Na','Mg','Al','Si',' P',' S','Cl','Ar',' K','Ca','Sc','Ti',