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tbgrad.h
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:
46 TBGrad(T&t, double ex = 1.0) : contribution(t), exchange_fraction(ex) {}
47 virtual ~TBGrad() {}
48
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: