********> bugfix.23
Author:   Bill Ross
Date:     6/12/95

Programs: Carnal

Severity: slight

Problem:  incorrect candidate hydrogen bond donors can be identified,
          generating superfluous output

Affects:  HBOND option with '94 force field

Cause:    Carnal relies on hard-coded force field information when
          identifying hbonding atoms. A new hydrogen type (H2) slipped
          through. 

Note:     Because Carnal depends on the force field, this problem 
          could always affect user-created atom types. Always check 
          your output, and don't create bondable non-carbon types
          beginning with 'C'!


Fix:  Make the following change to hbond.c
-----------------------------------------------------------------------
*** OLD hbond.c
--- NEW hbond.c
***************
*** 622,627
  		}
  
  		/*
  		 *  compare the bonded H to list of 'wrong' H types
  		 *	(HC, H4) which is shorter than list of 
  		 *	'right' types (H, HS, HO, HW, H3, H2)

--- 622,635 -----
  		}
  
  		/*
+ 		 *  as a quick test, rule out any donors that
+ 		 *	are carbon.. 1st char 'C' does the
+ 		 *	job for bondable atoms in '91, '94 force fields
+ 		 */
+ 		if (AtomSym[ATOMTOKLEN * hat] == 'C')
+ 			continue;
+ 
+ 		/*
  		 *  compare the bonded H to list of 'wrong' H types
  		 *	(HC, H2, H4) which is shorter than list of 
  		 *	'right' types (H, HS, HO, HW, H3, H2)
***************
*** 623,629
  
  		/*
  		 *  compare the bonded H to list of 'wrong' H types
! 		 *	(HC, H4) which is shorter than list of 
  		 *	'right' types (H, HS, HO, HW, H3, H2)
  		 */
  

--- 631,637 -----
  
  		/*
  		 *  compare the bonded H to list of 'wrong' H types
! 		 *	(HC, H2, H4) which is shorter than list of 
  		 *	'right' types (H, HS, HO, HW, H3, H2)
  		 */
  
***************
*** 629,635
  
  		hatch = AtomSym[ATOMTOKLEN * hyd + 1];
  	
! 		if (hatch == 'C'  ||  hatch == '4')
  			continue;
  
  		/*

--- 637,643 -----
  
  		hatch = AtomSym[ATOMTOKLEN * hyd + 1];
  	
! 		if (hatch == 'C'  ||  hatch == '2'  ||  hatch == '4')
  			continue;
  
  		/*
-----------------------------------------------------------------------

Temporary workarounds: restrict donor atoms considered to reasonable ones
		       using GROUP

--