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38 #ifndef GMX_MATH_UNITS_H
39 #define GMX_MATH_UNITS_H
44 * Physical constants to be used in Gromacs.
45 * No constants (apart from 0, 1 or 2) should
46 * be anywhere else in the code.
50 # define M_PI 3.14159265358979323846
54 # define M_PI_2 1.57079632679489661923
58 # define M_2PI 6.28318530717958647692
62 # define M_SQRT2 sqrt(2.0)
66 # define M_1_PI 0.31830988618379067154
69 #ifndef M_FLOAT_1_SQRTPI /* used in GPU kernels */
70 /* 1.0 / sqrt(M_PI) */
71 # define M_FLOAT_1_SQRTPI 0.564189583547756f
75 /* 1.0 / sqrt(M_PI) */
76 # define M_1_SQRTPI 0.564189583547756
80 /* 2.0 / sqrt(M_PI) */
81 # define M_2_SQRTPI 1.128379167095513
87 constexpr double c_angstrom = 1e-10;
88 constexpr double c_kilo = 1e3;
89 constexpr double c_nano = 1e-9;
90 constexpr double c_pico = 1e-12;
91 constexpr double c_nm2A = c_nano / c_angstrom;
92 constexpr double c_cal2Joule = 4.184; /* Exact definition of the calorie */
93 constexpr double c_electronCharge = 1.602176634e-19; /* Exact definition, Coulomb NIST 2018 CODATA */
95 constexpr double c_amu = 1.66053906660e-27; /* kg, NIST 2018 CODATA */
96 constexpr double c_boltzmann = 1.380649e-23; /* (J/K, Exact definition, NIST 2018 CODATA */
97 constexpr double c_avogadro = 6.02214076e23; /* 1/mol, Exact definition, NIST 2018 CODATA */
98 constexpr double c_universalGasConstant = c_boltzmann * c_avogadro; /* (J/(mol K)) */
99 constexpr double c_boltz = c_universalGasConstant / c_kilo; /* (kJ/(mol K)) */
100 constexpr double c_faraday = c_electronCharge * c_avogadro; /* (C/mol) */
101 constexpr double c_planck1 = 6.62607015e-34; /* J/Hz, Exact definition, NIST 2018 CODATA */
102 constexpr double c_planck = (c_planck1 * c_avogadro / (c_pico * c_kilo)); /* (kJ/mol) ps */
104 constexpr double c_epsilon0Si = 8.8541878128e-12; /* F/m, NIST 2018 CODATA */
105 /* Epsilon in our MD units: (e^2 / Na (kJ nm)) == (e^2 mol/(kJ nm)) */
106 constexpr double c_epsilon0 =
107 ((c_epsilon0Si * c_nano * c_kilo) / (c_electronCharge * c_electronCharge * c_avogadro));
109 constexpr double c_speedOfLight =
110 2.99792458e05; /* units of nm/ps, Exact definition, NIST 2018 CODATA */
112 constexpr double c_rydberg = 1.0973731568160e-02; /* nm^-1, NIST 2018 CODATA */
114 constexpr double c_one4PiEps0 = (1.0 / (4.0 * M_PI * c_epsilon0));
116 /* Pressure in MD units is:
117 * 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
119 constexpr double c_barMdunits = (1e5 * c_nano * c_pico * c_pico / c_amu);
120 constexpr double c_presfac = 1.0 / c_barMdunits;
122 /* c_debye2Enm should be (1e-21*c_pico)/(c_speedOfLight*c_electronCharge*c_nano*c_nano),
123 * but we need to factor out some of the exponents to avoid single-precision overflows.
125 constexpr double c_debye2Enm = (1e-15 / (c_speedOfLight * c_electronCharge));
126 constexpr double c_enm2Debye = 1.0 / c_debye2Enm;
128 /* to convert from a acceleration in (e V)/(amu nm) */
129 /* c_fieldfac is also Faraday's constant and c_electronCharge/(1e6 amu) */
130 constexpr double c_fieldfac = c_faraday / c_kilo;
132 /* to convert AU to MD units: */
133 constexpr double c_hartree2Kj = ((2.0 * c_rydberg * c_planck * c_speedOfLight) / c_avogadro);
134 constexpr double c_bohr2Nm = 0.0529177210903; /* nm^-1, NIST 2018 CODATA */
135 constexpr double c_hartreeBohr2Md = (c_hartree2Kj * c_avogadro / c_bohr2Nm);
137 constexpr double c_rad2Deg = 180.0 / M_PI;
138 constexpr double c_deg2Rad = M_PI / 180.0;
141 /* The four basic units */
142 #define unit_length "nm"
143 #define unit_time "ps"
144 #define unit_mass "u"
145 #define unit_energy "kJ/mol"
147 /* Temperature unit, T in this unit times c_boltz give energy in unit_energy */
148 #define unit_temp_K "K"
150 /* Charge unit, electron charge, involves c_one4PiEps0 */
151 #define unit_charge_e "e"
153 /* Pressure unit, pressure in basic units times c_presfac gives this unit */
154 #define unit_pres_bar "bar"
156 /* Dipole unit, debye, conversion from the unit_charge_e involves c_enm2Debye */
157 #define unit_dipole_D "D"
159 /* Derived units from basic units only */
160 #define unit_vel unit_length "/" unit_time
161 #define unit_volume unit_length "^3"
162 #define unit_invtime "1/" unit_time
164 /* Other derived units */
165 #define unit_surft_bar unit_pres_bar " " unit_length
167 /* SI units, conversion from basic units involves c_nano, c_pico and amu */
168 #define unit_length_SI "m"
169 #define unit_time_SI "s"
170 #define unit_mass_SI "kg"
172 #define unit_density_SI unit_mass_SI "/" unit_length_SI "^3"
173 #define unit_invvisc_SI unit_length_SI " " unit_time_SI "/" unit_mass_SI