92 lines
2.2 KiB
Plaintext
92 lines
2.2 KiB
Plaintext
#ifndef POTENTIALS_H
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#define POTENTIALS_H
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#include "precision.hpp"
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#include "vec3.h"
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#ifdef __CUDACC__
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#define CUDA_CALLABLE __host__ __device__
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#else
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#define CUDA_CALLABLE
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#endif
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/**
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* Result struct for the Pair Potential
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*/
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struct ForceAndEnergy {
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real energy;
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Vec3<real> force;
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CUDA_CALLABLE inline static ForceAndEnergy zero() {
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return {0.0, {0.0, 0.0, 0.0}};
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};
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};
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/**
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* Abstract implementation of a Pair Potential.
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* Pair potentials are potentials which depend solely on the distance
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* between two particles. These do not include multi-body potentials such as
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* EAM
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*
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*/
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struct PairPotential {
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real m_rcutoffsq;
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PairPotential(real rcutoff) : m_rcutoffsq(rcutoff * rcutoff) {};
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#ifdef __CUDACC__
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CUDA_CALLABLE ~PairPotential();
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#else
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virtual ~PairPotential() = 0;
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#endif
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/**
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* Calculate the force and energy for a specific atom pair based on a
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* displacement vector r.
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*/
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CUDA_CALLABLE virtual ForceAndEnergy calc_force_and_energy(Vec3<real> r) = 0;
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};
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/**
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* Calculate the Lennard-Jones energy and force for the current particle pair
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* described by displacement vector r
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*/
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struct LennardJones : PairPotential {
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real m_epsilon;
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real m_sigma;
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CUDA_CALLABLE LennardJones(real sigma, real epsilon, real rcutoff)
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: PairPotential(rcutoff), m_epsilon(epsilon), m_sigma(sigma) {};
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CUDA_CALLABLE ForceAndEnergy calc_force_and_energy(Vec3<real> r) {
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real rmagsq = r.squared_norm2();
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if (rmagsq < this->m_rcutoffsq && rmagsq > 0.0) {
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real inv_rmag = 1 / std::sqrt(rmagsq);
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// Pre-Compute the terms (doing this saves on multiple devisions/pow
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// function call)
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real sigma_r = m_sigma * inv_rmag;
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real sigma_r6 = sigma_r * sigma_r * sigma_r * sigma_r * sigma_r * sigma_r;
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real sigma_r12 = sigma_r6 * sigma_r6;
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// Get the energy
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real energy = 4.0 * m_epsilon * (sigma_r12 - sigma_r6);
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// Get the force vector
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real force_mag =
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4.0 * m_epsilon *
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(12.0 * sigma_r12 * inv_rmag - 6.0 * sigma_r6 * inv_rmag);
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Vec3<real> force = r.scale(force_mag * inv_rmag);
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return {energy, force};
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} else {
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return ForceAndEnergy::zero();
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}
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};
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CUDA_CALLABLE ~LennardJones(){};
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};
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PairPotential::~PairPotential() {};
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#endif
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