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Merge pull request #1637 from glotzerlab/external_magnetic_field
External magnetic field
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| // Copyright (c) 2009-2023 The Regents of the University of Michigan. | ||
| // Part of HOOMD-blue, released under the BSD 3-Clause License. | ||
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| #ifndef __EVALUATOR_EXTERNAL_MAGNETIC_FIELD_H__ | ||
| #define __EVALUATOR_EXTERNAL_MAGNETIC_FIELD_H__ | ||
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| #ifndef __HIPCC__ | ||
| #include <string> | ||
| #endif | ||
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| #include "hoomd/BoxDim.h" | ||
| #include "hoomd/HOOMDMath.h" | ||
| #include "hoomd/VectorMath.h" | ||
| #include <math.h> | ||
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| /*! \file EvaluatorExternalMagneticField.h | ||
| \brief Defines the external potential evaluator to induce a magnetic field | ||
| */ | ||
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| // need to declare these class methods with __device__ qualifiers when building in nvcc | ||
| // DEVICE is __host__ __device__ when included in nvcc and blank when included into the host | ||
| // compiler | ||
| #ifdef __HIPCC__ | ||
| #define DEVICE __device__ | ||
| #else | ||
| #define DEVICE | ||
| #endif | ||
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| namespace hoomd | ||
| { | ||
| namespace md | ||
| { | ||
| //! Class for evaluating an magnetic field | ||
| /*! <b>General Overview</b> | ||
| The external potential \f$V(\theta) \f$ is implemented using the following formula: | ||
| \f[ | ||
| V(\theta}) = - \vec{B} \cdot \vec{n}_i(\theta) | ||
| \f] | ||
| where \f$B\f$ is the strength of the magnetic field and \f$\vec{n}_i\f$ is the magnetic moment | ||
| of particle i. | ||
| */ | ||
| class EvaluatorExternalMagneticField | ||
| { | ||
| public: | ||
| //! type of parameters this external potential accepts | ||
| struct param_type | ||
| { | ||
| Scalar3 B; | ||
| Scalar3 mu; | ||
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| #ifndef __HIPCC__ | ||
| param_type() : B(make_scalar3(0, 0, 0)), mu(make_scalar3(0, 0, 0)) { } | ||
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| param_type(pybind11::dict params) | ||
| { | ||
| pybind11::tuple py_B = params["B"]; | ||
| B.x = pybind11::cast<Scalar>(py_B[0]); | ||
| B.y = pybind11::cast<Scalar>(py_B[1]); | ||
| B.z = pybind11::cast<Scalar>(py_B[2]); | ||
| pybind11::tuple py_mu = params["mu"]; | ||
| mu.x = pybind11::cast<Scalar>(py_mu[0]); | ||
| mu.y = pybind11::cast<Scalar>(py_mu[1]); | ||
| mu.z = pybind11::cast<Scalar>(py_mu[2]); | ||
| } | ||
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| pybind11::dict toPython() | ||
| { | ||
| pybind11::dict d; | ||
| d["B"] = pybind11::make_tuple(B.x, B.y, B.z); | ||
| d["mu"] = pybind11::make_tuple(mu.x, mu.y, mu.z); | ||
| return d; | ||
| } | ||
| #endif // ifndef __HIPCC__ | ||
| } __attribute__((aligned(16))); | ||
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| typedef void* field_type; | ||
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| //! Constructs the external field evaluator | ||
| /*! \param X position of particle | ||
| \param box box dimensions | ||
| \param params per-type parameters of external potential | ||
| */ | ||
| DEVICE EvaluatorExternalMagneticField(Scalar3 X, | ||
| quat<Scalar> q, | ||
| const BoxDim& box, | ||
| const param_type& params, | ||
| const field_type& field) | ||
| : m_q(q), m_B(params.B), m_mu(params.mu) | ||
| { | ||
| } | ||
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| DEVICE static bool isAnisotropic() | ||
| { | ||
| return true; | ||
| } | ||
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| //! ExternalMagneticField needs charges | ||
| DEVICE static bool needsCharge() | ||
| { | ||
| return false; | ||
| } | ||
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| //! Accept the optional charge value | ||
| /*! \param qi Charge of particle i | ||
| */ | ||
| DEVICE void setCharge(Scalar qi) { } | ||
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| //! Declares additional virial contributions are needed for the external field | ||
| /*! No contribution | ||
| */ | ||
| DEVICE static bool requestFieldVirialTerm() | ||
| { | ||
| return false; | ||
| } | ||
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| //! Evaluate the force, energy and virial | ||
| /*! \param F force vector | ||
| \param T torque vector | ||
| \param energy value of the energy | ||
| \param virial array of six scalars for the upper triangular virial tensor | ||
| */ | ||
| DEVICE void | ||
| evalForceTorqueEnergyAndVirial(Scalar3& F, Scalar3& T, Scalar& energy, Scalar* virial) | ||
| { | ||
| vec3<Scalar> dir = rotate(m_q, m_mu); | ||
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| vec3<Scalar> T_vec = cross(dir, m_B); | ||
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| T.x = T_vec.x; | ||
| T.y = T_vec.y; | ||
| T.z = T_vec.z; | ||
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| energy = -dot(dir, m_B); | ||
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| F.x = Scalar(0.0); | ||
| F.y = Scalar(0.0); | ||
| F.z = Scalar(0.0); | ||
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| for (unsigned int i = 0; i < 6; i++) | ||
| virial[i] = Scalar(0.0); | ||
| } | ||
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| #ifndef __HIPCC__ | ||
| //! Get the name of this potential | ||
| /*! \returns The potential name. | ||
| */ | ||
| static std::string getName() | ||
| { | ||
| return std::string("b_field"); | ||
| } | ||
| #endif | ||
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| protected: | ||
| quat<Scalar> m_q; //!< Particle orientation | ||
| vec3<Scalar> m_B; //!< Magnetic field vector (box frame). | ||
| vec3<Scalar> m_mu; //!< Magnetic dipole moment (particle frame). | ||
| }; | ||
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| } // end namespace md | ||
| } // end namespace hoomd | ||
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| #endif // __EVALUATOR_EXTERNAL_LAMELLAR_H__ |
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