class forcefields::PotentialBase¶

Overview¶

Functions and tools commonly used by potentials. Contains functions for quadratic retrainst, Lennard-Jones, Coulomb, to manage the periodic boundaries and interface for cutoff. The system of units used is (eV, Angstrom, fs, e). Rules to combine different Lennard-Jones parameters were taken from:

Unlike Lennard-Jones Parameters for Vapor-Liquid Equilibria, Thorsten Schnabel, Jadran Vrabec , Hans Hasse, Institut fur Technische Thermodynamik und Thermische Verfahrenstechnik, Universitat Stuttgart, D-70550 Stuttgart, Germany, http://www.itt.uni-stuttgart.de/~schnabel/CR.pdf. More…

class PotentialBase {
public:
    // structs
 
    template <int N, class R = double(*const)[N], class F = double(*const)[N]>
    struct ChargeGroup;
 
    struct Vector3;
 
    // construction
 
    PotentialBase();
    PotentialBase(double cutoff, double switchingWidth);
    virtual ~PotentialBase();
 
    // methods
 
    double getSwitchingWidth() const;
    void setSwitchingWidth(double width);
    double getCutoff() const;
    void setCutoff(double cutoff);
    static double applyPeriodicity0(double r, double const period);
    static void applyPeriodicity0(double r[], double const periods[]);
};

Detailed Documentation¶

Construction¶

PotentialBase()

Non bond interaction cutoff. When the distance between two molecules is over getCutoff(), van der Waals and Coulomb interactions between the two molecules are ignored.

Methods¶

double getSwitchingWidth() const

Width of the switching zone. In the switching zone the potential is replaced by \(V=U\times S(x)\) where U is the real potential V the switching potential and S the switching function. Variable x=0 at the beginning of the switching zone and x=1 at the end the function S is \(S=2x^3-3x^2+1\) which has the following properties: S(0)=1, S(1)=0, S’(0)=0 and S’(1)=0. The switching when the distance between the two molecules is getCutoff()- getSwitchingWidth() and ends when the distance is getCutoff();

See also:

getCutoff().

static double applyPeriodicity0(double r, double const period)

Minimum image representation.

Parameters:

r	Cyclic coordinate.
period	Period of the coordinates.

Returns:

Minimum image representation of r. The value returned is \(\frac{-period}{2} \le r \le \frac{period}{2}\)

static void applyPeriodicity0(double r[], double const periods[])

Minimum image representation. Writes the minimum image of r in place. Each component satisfies \(\frac{-period}{2} \le r_i \le \frac{period}{2}\).

Parameters:

r	Three-dimension vector.
periods	Three-dimension vector containing periods along each of the axes.