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/* |
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* Copyright (C) 2000-2004 Object Oriented Parallel Simulation Engine (OOPSE) project |
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* |
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* Contact: oopse@oopse.org |
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* |
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* This program is free software; you can redistribute it and/or |
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* modify it under the terms of the GNU Lesser General Public License |
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* as published by the Free Software Foundation; either version 2.1 |
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* of the License, or (at your option) any later version. |
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* All we ask is that proper credit is given for our work, which includes |
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* - but is not limited to - adding the above copyright notice to the beginning |
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* of your source code files, and to any copyright notice that you may distribute |
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* with programs based on this work. |
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* |
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* This program is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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* GNU Lesser General Public License for more details. |
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* |
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* You should have received a copy of the GNU Lesser General Public License |
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* along with this program; if not, write to the Free Software |
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
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* |
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*/ |
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#include "types/CharmmTorsionType.hpp" |
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namespace oopse { |
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void CharmmTorsionType::calcForce(double cosPhi, double sinPhi, double& V, double& dVdPhi) { |
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V = 0; |
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dVdPhi = 0; |
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double phi = -atan2(sinPhi, cosPhi); |
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std::vector<CharmmTorsionParameter>::iterator i; |
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for (i = parameter_.begin(); i != parameter_.end(); ++i) { |
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double kchi= i->kchi; |
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int n = i->n; |
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double delta = i->delta; |
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if (n == 0) { |
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//if periodicity is equal to 0, use harmonic form |
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double diff = phi - delta; |
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if (diff < -OOPSEConstant::PI) { |
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diff += OOPSEConstant::TWOPI; |
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} else if (diff > OOPSEConstant::PI) { |
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diff -= OOPSEConstant::TWOPI; |
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} |
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V += kchi * diff * diff; |
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dVdPhi += 2.0 * kchi * diff; |
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} else { |
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//use normal cos form if periodicity is greater than 0 |
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V += kchi * (1 + cos(n * phi + delta)); |
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dVdPhi += -n * kchi * sin(n * phi + delta); |
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} |
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} |
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} |
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} //end namespace oopse |
