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  Purpose : Diagonalizes the Hamiltonian matrix calculated by fmat.
  Usage   : diag [-d -o -lo -hi -n -t -es -e -u -w -ver -h -?] mtt_ovl 
                   mtt_ham [[mtt_ovl_2] [mtt_ham_2]].

 Options  : 
 -d PATH  : The output is directed to PATH rather than to the current directory.
            The string PATH may be a relative or a full path-name.
            If PATH=no, i.e. "-d no", no output files will be opened.
 -o NAME  : Change the name of output file from "diag" to NAME.
 -lo klo  : Take matrix elements in Mtt files only from the klo-th index. 
 -hi khi  : Take matrix elements in Mtt files only up to the khi-th index. 
 -n step  : Take only every n-th step of the Mtt matrix elements. 
 -t       : Expand the nXn mtt-matrix to (2n-1)X(2n-1) one including negative 
            times. In this case the second set of overlap and Hamiltonian 
            matrices are needed.
 -es eps  : Set cut-off parameter for eigenvalues. Default is eps=1.e-10
 -e E unit: The offset energy is set to E unit.
            Note: "-e lsth" is equivalent to "-e 4.74746 ev".
                  "-e co2" is equivalent to "-e -2534.5298 cm-1".
 -u UNIT  : Set the output energy unit to UNIT. Default is au.
 -w       : Overwrite an existing "diag" file.
 -ver     : Version information about the program 
 -h       : Print this help text. 
 -?       : Print this help text. 
 The arguments "mtt_ovl" and "mtt_ham" are the Overlap- and Hamiltonian 
 matrix files calculated by the "fmat" program. If "-t" option is used, 
 the second set of Overlap- and  Hamiltonian matrices with different 
 scalar product is needed.

 Examples  : diag -es 1.0e-8_dop -hi 60  mtt_h mtt_H1_h 
           : diag -hi 40 -n 2 -t mtt_h mtt_H1_h  mtt_s mtt_H1_s
 Important note: Both overlap and Hamiltonian-matrices should be calculated 
                 either as hermitian or as symmetric scalar products.
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