Program Documentation for "GDIIS"                          
                         Written by Peter Szalay                                
                         Revision Date: 31-jan-89                               
                                                                                
Program "GDIIS" performs the transformation of the cartesian forces             
and coordinates into the internal ones and controls the geometry                
optimization procedur. For the algorithm see P.Csaszar and P.Pulay              
J.Mol.Struct. 31,114(1984).                                                     
                                                                                
unit  file name  description                                                    
----  ---------  ----------------                                               
( 5)             user input file.                                               
( 6)             listing file.                                                  
(31)  'GEOMFL'   Contains the cartesian coordinates and in the first            
                 iteration also the Hessian-matrix. After run it                
                 contains the new coordinates.                                  
(32)  'CARTGRD'  Contains the cartesian forces.                                 
(33)  'GDIISFL'  Contains the information about the preceeding iteration        
                 (displacements, forces, coordinates, hessian-matrix).          
                 It will be first produced in the first iteration and           
                 will be modyfied in all other iterations.                      
(34)  'SCRFL'    Scratch file.                                                  
                                                                                
                             **************                                     
                             * User Input *                                     
                             **************                                     
                                                                                
The required user input is read from the input file using                       
format (A4,6X,F10.5). The control varibles are:                                 
                                                                                
MOLE /it folows by a title. Have to be the first card.                          
                                                                                
GDII /it folows by the number of points used in the extrapolation.              
Default is NQ+1 (NQ is the nuber of internal coordinates) but <21.              
                                                                                
TOL  /10**TOL is convergence threshold for the displacemets. Default            
is 4 (0.0001 A).                                                                
                                                                                
FIXC /coordinates which will not be optimized. for each coordinate an           
extra card required!                                                            
                                                                                
CARD /number of symmetry different atoms.                                       
                                                                                
FMAT /Option for the hessian matrix. 0: unit matrix 1: only diagonal            
elements 2: complete hessian matrix. (The input hessian matrix  is              
contained on the GEOMFL file after the coordinates. It is nessesary             
only for the first iteration. see GDIISFL file). Deafult is 0.                  
                                                                                
BMAT /only relaxation (without GDIIS extrapolation) will be performed.          
                                                                                
K    /begins the definition of internal coordinats (see BMAT program).          
                                                                                
STOP /last input card.