geoOptCell.h

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// ---------------------------------------------------------------------
//
// Copyright (c) 2017-2025  The Regents of the University of Michigan and DFT-FE
// authors.
//
// This file is part of the DFT-FE code.
//
// The DFT-FE code is free software; you can use it, redistribute
// it, and/or modify it under the terms of the GNU Lesser General
// Public License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// The full text of the license can be found in the file LICENSE at
// the top level of the DFT-FE distribution.
//
// ---------------------------------------------------------------------
 
#ifndef geoOptCell_H_
#define geoOptCell_H_
#include "constants.h"
#include "nonlinearSolverProblem.h"
#include "nonLinearSolver.h"
#include "dftBase.h"
#include "dftfeWrapper.h"
 
namespace dftfe
{
  /**
   * @brief problem class for cell stress relaxation solver.
   *
   * @author Sambit Das
   */
  class geoOptCell : public nonlinearSolverProblem
  {
  public:
    /** @brief Constructor.
     *
     *  @param _dftPtr pointer to dftClass
     *  @param mpi_comm_parent parent mpi_communicator
     */
    geoOptCell(dftBase        *dftPtr,
               const MPI_Comm &mpi_comm_parent,
               const bool      restart = false);
 
    /**
     * @brief initializes the data member d_relaxationFlags.
     *
     */
    void
    init(const std::string &restartPath);
 
    /**
     * @brief calls the cell stress relaxation solver.
     *
     * The Polak–Ribière nonlinear CG solver with secant based line search
     * is used for the stress relaxation.
     *
     * @return dftfe::Int total geometry update calls
     */
    dftfe::Int
    run();
 
    /**
     * @brief writes the current fem mesh.
     *
     */
    void
    writeMesh(std::string meshFileName);
 
    /**
     * @brief Obtain number of unknowns (depends on the stress relaxation constraint type).
     *
     * @return dftfe::Int Number of unknowns.
     */
    dftfe::uInt
    getNumberUnknowns() const;
 
    /**
     * @brief Compute function gradient (stress).
     *
     * @param gradient STL vector for gradient values.
     */
    void
    gradient(std::vector<double> &gradient);
 
    /**
     * @brief Update the strain tensor epsilon.
     *
     * The new strain tensor is epsilonNew= epsilon+ delta(epsilon). Since
     * epsilon strain is already applied to the domain. The new strain to be
     * applied to the domain is epsilonNew*inv(epsilon)
     *
     * @param solution delta(epsilon).
     */
    void
    update(const std::vector<double> &solution,
           const bool                 computeStress      = true,
           const bool useSingleAtomSolutionsInitialGuess = false);
 
    /**
     * @brief create checkpoint file for current domain bounding vectors and atomic coordinates.
     *
     */
    void
    save();
 
    /**
     * @brief check for convergence.
     *
     */
    bool
    isConverged() const;
 
    const MPI_Comm &
    getMPICommunicator();
 
    /// Not implemented
    void
    value(std::vector<double> &functionValue);
 
    /// Not implemented
    void
    precondition(std::vector<double> &s, const std::vector<double> &gradient);
 
    /// Not implemented
    void
    solution(std::vector<double> &solution);
 
    /// Not implemented
    std::vector<dftfe::uInt>
    getUnknownCountFlag() const;
 
  private:
    /// Relaxation flags which determine whether a particular stress component
    /// is to be relaxed or not.
    //  The relaxation flags are determined based on the stress relaxation
    //  constraint type.
    std::vector<dftfe::uInt> d_relaxationFlags;
 
    std::string d_restartPath;
    std::string d_solverRestartPath;
    bool        d_isRestart;
    bool        d_solverRestart;
    bool        d_isScfRestart;
    dftfe::Int  d_solver;
    /// total number of calls to update()
    dftfe::Int d_totalUpdateCalls;
    double     d_domainVolumeInitial;
    /// current strain tensor applied on the domain
    dealii::Tensor<2, 3, double> d_strainEpsilon;
 
    /// pointer to dft class
    dftBase                         *d_dftPtr;
    std::unique_ptr<nonLinearSolver> d_nonLinearSolverPtr;
 
    /// parallel communication objects
    const MPI_Comm    mpi_communicator;
    const dftfe::uInt n_mpi_processes;
    const dftfe::uInt this_mpi_process;
 
    /// conditional stream object
    dealii::ConditionalOStream pcout;
  };
 
} // namespace dftfe
 
#endif