1 //
2 // tbgrad.h --- definition of the abstract two-electron gradient builder
3 //
4 // Copyright (C) 1996 Limit Point Systems, Inc.
5 //
6 // Author: Edward Seidl <seidl@janed.com>
7 // Maintainer: LPS
8 //
9 // This file is part of the SC Toolkit.
10 //
11 // The SC Toolkit is free software; you can redistribute it and/or modify
12 // it under the terms of the GNU Library General Public License as published by
13 // the Free Software Foundation; either version 2, or (at your option)
14 // any later version.
15 //
16 // The SC Toolkit is distributed in the hope that it will be useful,
17 // but WITHOUT ANY WARRANTY; without even the implied warranty of
18 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
19 // GNU Library General Public License for more details.
20 //
21 // You should have received a copy of the GNU Library General Public License
22 // along with the SC Toolkit; see the file COPYING.LIB.  If not, write to
23 // the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
24 //
25 // The U.S. Government is granted a limited license as per AL 91-7.
26 //
27 
28 #ifndef _chemistry_qc_scf_tbgrad_h
29 #define _chemistry_qc_scf_tbgrad_h
30 
31 #ifdef __GNUC__
32 #pragma interface
33 #endif
34 
35 #include <util/group/thread.h>
36 
37 namespace sc {
38 
39 template<class T>
40 class TBGrad : public Thread {
41   protected:
42     T& contribution;
43     double exchange_fraction;
44 
45   public:
contribution(t)46     TBGrad(T&t, double ex = 1.0) : contribution(t), exchange_fraction(ex) {}
~TBGrad()47     virtual ~TBGrad() {}
48 
set_scale(double & coulombscale,double & exchangescale,int i,int j,int k,int l)49     inline void set_scale(double& coulombscale, double& exchangescale,
50                           int i, int j, int k, int l) const
51     {
52       double scale = 1.0;
53 
54       if ((i!=k)||(j!=l))
55         scale *= 2.0;
56 
57       if (i!=j)
58         scale *= 2.0;
59 
60       coulombscale = 0.5*scale;
61       exchangescale = -0.25*scale * exchange_fraction;
62 
63       if (k!=l)
64         coulombscale *= 2.0;
65 
66       if ((k!=l)&&(i==j))
67         exchangescale *= 2.0;
68     }
69 };
70 
71 }
72 
73 #endif
74 
75 // Local Variables:
76 // mode: c++
77 // c-file-style: "ETS"
78 // End:
79