src/gromacs/math/units.h

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  37 #ifndef GMX_MATH_UNITS_H
  38 #define GMX_MATH_UNITS_H
  39
  40 /*
  41  * Physical constants to be used in Gromacs.
  42  * No constants (apart from 0, 1 or 2) should
  43  * be anywhere else in the code.
  44  */
  45
  46 #include "gromacs/math/utilities.h"
  47
  48 #ifdef __cplusplus
  49 extern "C" {
  50 #endif
  51
  52 #define ANGSTROM         (1e-10)                           /* Old...    */
  53 #define KILO             (1e3)                             /* Thousand  */
  54 #define NANO             (1e-9)                            /* A Number  */
  55 #define PICO             (1e-12)                           /* A Number  */
  56 #define A2NM             (ANGSTROM/NANO)                   /* NANO              */
  57 #define NM2A             (NANO/ANGSTROM)                   /* 10.0              */
  58 #define RAD2DEG          (180.0/M_PI)                      /* Conversion        */
  59 #define DEG2RAD          (M_PI/180.0)                      /* id                */
  60 #define CAL2JOULE        (4.184)                           /* id                */
  61 #define E_CHARGE         (1.602176565e-19)                 /* Coulomb, NIST 2010 CODATA */
  62
  63 #define AMU              (1.660538921e-27)                 /* kg, NIST 2010 CODATA  */
  64 #define BOLTZMANN        (1.3806488e-23)                   /* (J/K, NIST 2010 CODATA */
  65 #define AVOGADRO         (6.02214129e23)                   /* no unit, NIST 2010 CODATA */
  66 #define RGAS             (BOLTZMANN*AVOGADRO)              /* (J/(mol K))  */
  67 #define BOLTZ            (RGAS/KILO)                       /* (kJ/(mol K)) */
  68 #define FARADAY          (E_CHARGE*AVOGADRO)               /* (C/mol)      */
  69 #define ELECTRONVOLT     (E_CHARGE*AVOGADRO/KILO)          /* (kJ/mol)   */
  70 #define PLANCK1          (6.62606957e-34)                  /* J s, NIST 2010 CODATA */
  71 #define PLANCK           (PLANCK1*AVOGADRO/(PICO*KILO))    /* (kJ/mol) ps */
  72
  73 #define EPSILON0_SI      (8.854187817e-12)                 /* F/m,  NIST 2010 CODATA */
  74 /* Epsilon in our MD units: (e^2 / Na (kJ nm)) == (e^2 mol/(kJ nm)) */
  75 #define EPSILON0         (EPSILON0_SI*NANO*KILO)/(E_CHARGE*E_CHARGE*AVOGADRO)
  76
  77 #define SPEED_OF_LIGHT   (2.99792458E05)                   /* nm/ps, NIST 2010 CODATA */
  78 #define ATOMICMASS_keV   (931494.061)                      /* Atomic mass in keV, NIST 2010 CODATA   */
  79 #define ELECTRONMASS_keV (510.998928)                      /* Electron mas in keV, NIST 2010 CODATA  */
  80
  81 #define RYDBERG          (1.0973731568539e-02)             /* nm^-1, NIST 2010 CODATA */
  82
  83 #define ONE_4PI_EPS0     (1.0/(4.0*M_PI*EPSILON0))
  84 #define FACEL            10.0*ONE_4PI_EPS0
  85
  86 /* Pressure in MD units is:
  87  * 1 bar = 1e5 Pa = 1e5 kg m^-1 s^-2 = 1e-28 kg nm^-1 ps^-2 = 1e-28 / AMU amu nm^1 ps ^2
  88  */
  89 #define BAR_MDUNITS      (1e5*NANO*PICO*PICO/AMU)
  90 #define PRESFAC          (1.0/BAR_MDUNITS)
  91
  92 /* DEBYE2ENM should be (1e-21*PICO)/(SPEED_OF_LIGHT*E_CHARGE*NANO*NANO),
  93  * but we need to factor out some of the exponents to avoid single-precision overflows.
  94  */
  95 #define DEBYE2ENM        (1e-15/(SPEED_OF_LIGHT*E_CHARGE))
  96 #define ENM2DEBYE        (1.0/DEBYE2ENM)
  97
  98 /* to convert from a acceleration in (e V)/(amu nm) */
  99 /* FIELDFAC is also Faraday's constant and E_CHARGE/(1e6 AMU) */
 100 #define FIELDFAC         (FARADAY/KILO)
 101
 102 /* to convert AU to MD units: */
 103 #define HARTREE2KJ       ((2.0*RYDBERG*PLANCK*SPEED_OF_LIGHT)/AVOGADRO)
 104 #define BOHR2NM          (0.052917721092)                  /* nm^-1, NIST 2010 CODATA */
 105 #define HARTREE_BOHR2MD  (HARTREE2KJ*AVOGADRO/BOHR2NM)
 106
 107
 108 /* The four basic units */
 109 #define unit_length   "nm"
 110 #define unit_time     "ps"
 111 #define unit_mass     "u"
 112 #define unit_energy   "kJ/mol"
 113
 114 /* Temperature unit, T in this unit times BOLTZ give energy in unit_energy */
 115 #define unit_temp_K   "K"
 116
 117 /* Charge unit, electron charge, involves ONE_4PI_EPS0 */
 118 #define unit_charge_e "e"
 119
 120 /* Pressure unit, pressure in basic units times PRESFAC gives this unit */
 121 #define unit_pres_bar "bar"
 122
 123 /* Dipole unit, debye, conversion from the unit_charge_e involves ENM2DEBYE */
 124 #define unit_dipole_D "D"
 125
 126 /* Derived units from basic units only */
 127 #define unit_vel      unit_length "/" unit_time
 128 #define unit_volume   unit_length "^3"
 129 #define unit_invtime  "1/" unit_time
 130
 131 /* Other derived units */
 132 #define unit_surft_bar unit_pres_bar " " unit_length
 133
 134 /* SI units, conversion from basic units involves NANO, PICO and AMU */
 135 #define unit_length_SI  "m"
 136 #define unit_time_SI    "s"
 137 #define unit_mass_SI    "kg"
 138
 139 #define unit_density_SI unit_mass_SI "/" unit_length_SI "^3"
 140 #define unit_invvisc_SI unit_length_SI " " unit_time_SI "/" unit_mass_SI
 141
 142 /* The routines below can be used for converting units from or to GROMACS
 143    internal units. */
 144 enum {
 145     eg2cAngstrom, eg2cNm, eg2cBohr, eg2cKcal_Mole,
 146     eg2cHartree, eg2cHartree_e, eg2cAngstrom3, eg2cCoulomb,
 147     eg2cDebye, eg2cElectron, eg2cBuckingham, eg2cNR
 148 };
 149
 150 /* Convert value x to GROMACS units. Energy -> Energy, Length -> Length etc.
 151    The type of x is deduced from unit,
 152    which should be taken from the enum above. */
 153 extern double convert2gmx(double x, int unit);
 154
 155 /* Convert value x from GROMACS units to the desired one.
 156    The type of return value is deduced from unit, see above */
 157 extern double gmx2convert(double x, int unit);
 158
 159 /* Convert the string to one of the units supported. Returns -1 if not found. */
 160 extern int string2unit(char *string);
 161
 162 /* Convert the unit to a string. Return NULL when unit is out of range. */
 163 extern const char *unit2string(int unit);
 164
 165 #ifdef __cplusplus
 166 }
 167 #endif
 168
 169 #endif