src/gromacs/ewald/ewald_utils.h

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  37 /*! \libinternal \file
  38  *
  39  * \brief Declares utility functions related to Ewald.
  40  *
  41  * \author Mark Abraham <mark.j.abraham@gmail.com>
  42  * \author Szilárd Páll <pall.szilard@gmail.com>
  43  *
  44  * \inlibraryapi
  45  * \ingroup module_ewald
  46  */
  47 #ifndef GMX_EWALD_UTILS_H
  48 #define GMX_EWALD_UTILS_H
  49
  50 #include "gromacs/math/vec.h"
  51 #include "gromacs/mdtypes/inputrec.h"
  52 #include "gromacs/pbcutil/pbc.h"
  53 #include "gromacs/utility/gmxassert.h"
  54 #include "gromacs/utility/real.h"
  55
  56 /*! \brief Computes the Ewald splitting coefficient for Coulomb
  57  *
  58  * Returns a value of beta that satisfies rtol > erfc(beta * rc)
  59  * (and is very close to equality). That value is used the same way in
  60  * all Coulomb-based Ewald methods.
  61  *
  62  * \param[in] rc    Cutoff radius
  63  * \param[in] rtol  Required maximum value of the short-ranged
  64  *                  potential at the cutoff (ie. ewald-rtol)
  65  * \return          The value of the splitting coefficient that
  66  *                  produces the required dtol at rc.
  67  */
  68 real calc_ewaldcoeff_q(real rc, real rtol);
  69
  70 /*! \brief Computes the Ewald splitting coefficient for LJ
  71  *
  72  * Returns a value of beta that satisfies dtol > erfc(beta * rc) * (1
  73  * + beta^2 * rc^2 + 0.5 * beta^4 * rc^4) (and is very close to
  74  * equality), which is used in LJ-PME.
  75  *
  76  * \param[in] rc    Cutoff radius
  77  * \param[in] rtol  Required maximum value of the short-ranged
  78  *                  potential at the cutoff (ie. ewald-rtol-lj)
  79  * \return          The value of the splitting coefficient that
  80  *                  produces the required dtol at rc.
  81  */
  82 real calc_ewaldcoeff_lj(real rc, real rtol);
  83
  84
  85 /*! \libinternal \brief Class to handle box scaling for Ewald and PME.
  86  *
  87  * At construction contents of inputrec determine whether scaling is necessary
  88  * as well as the scaling factor used. Later, the scaleBox method can be used
  89  * to apply the appropriate scaling (if needed) for Ewald-based methods.
  90  *
  91  */
  92 class EwaldBoxZScaler
  93 {
  94
  95 private:
  96     bool scaleWithWalls_; /**< True if the simulation uses two walls and the box needs to be scaled in PME */
  97     real scalingFactor_; /**< Box The scaling factor PME uses with walls */
  98
  99 public:
 100     EwaldBoxZScaler() = delete;
 101
 102     /*! \brief Constructor that takes the input record to initialize Ewald box scaling appropriately. */
 103     EwaldBoxZScaler(const t_inputrec& ir)
 104     {
 105         if (inputrecPbcXY2Walls(&ir))
 106         {
 107             scaleWithWalls_ = true;
 108             scalingFactor_  = ir.wall_ewald_zfac;
 109         }
 110         else
 111         {
 112             scaleWithWalls_ = false;
 113             scalingFactor_  = 1;
 114         }
 115     }
 116
 117     /*! \brief Copy and scale the box for PME.
 118      *
 119      * When PME is used with 2D periodicity and two walls, the
 120      * copy of the \p box passed is scaled with the Z scaling factor.
 121      *
 122      * \param[in] box        The current box matrix
 123      * \param[out] scaledBox Scaled copy of the box matrix.
 124      */
 125     void scaleBox(const matrix box, matrix scaledBox)
 126     {
 127         GMX_ASSERT(box, "invalid source box pointer");
 128         GMX_ASSERT(scaledBox, "invalid target box pointer");
 129
 130         copy_mat(box, scaledBox);
 131         if (scaleWithWalls_)
 132         {
 133             svmul(scalingFactor_, scaledBox[ZZ], scaledBox[ZZ]);
 134         }
 135     }
 136 };
 137
 138 #endif