Question

我正在尝试计算盒子中粒子之间的距离。如果计算的距离大于预设的截止距离，则势能为0.否则，为1.

我认为有一些舍入问题，我不熟悉变量类型，并通过函数传递变量以了解下一步该做什么。

错误

当我手动计算d0时，我得到d0 = 0.070 - 这不是计算机得到的！计算机获得的数量为e-310。
所有计算出的距离（dij）都不小于1/14，远远大于e-310。根据我的if语句，如果dij> d0，那么U = 0，所以我应该得到总能量0，但这就是我得到的：

d0是6.95322e-310

我是0 j是1 dij是0.0714286 d0是6.95322e-310 Uij是1

.....

系统能量为24976

如果我能提供更多信息，请告诉我。我没有包含我的全部代码，但另一部分不涉及d0的操作。

我复制了下面的相关代码

第1部分：相关的框数据 class Vector { 上市：双x; 双y; Vector（）{

    }
    Vector (double x_, double y_) {
        x = x_;
        y = y_;
    }
    double len() {
        return sqrt(x*x + y*y);
    }
    double lenSqr() {
        return x*x + y*y;
    }
};
class Atom 
{
    public:
        Vector pos;
        Vector vel;
        Vector force;
        Atom (double x_, double y_) {
        pos = Vector(x_, y_);
        }

};

class BoxData
{
    public:
        const double Len = 1.;
        const double LenHalf = 0.5 * Len;
        long double d = 1. / 14; // d is the distance between each atom 
        in the initial trigonal lattice
        int nu = 7; // auxillary parameter - will be varied
        long double d0 = d * (1 - 2^(nu - 8)); // cutoff distance
        double alpha = d - d0; // maximum allowed displacement
};
int main() {

// Initialize box
LoadBox();

// Institute a for loop here
SystemEnergy();
MonteCarloMove();

return 0;

}

//Putting atoms into box
void LoadBox()
{
ofstream myfile("init.dat", ios::out);

//Load atoms in box in triangular offset lattice
const double x_shift  = 1. / 14;
const double y_shift  = 1. / 16;
double x = 0;
double y = 0;
double x_offset = 0;

for (y = 0; y <= 1. - y_shift; y += y_shift) {
    for (x = x_offset; x < 0.99; x += x_shift) {
        // create atom in position (x, y)
        // and store it in array of atoms
        atoms.push_back(Atom(x, y));
    }
    // every new row flip offset 0 -> 1/28 -> 0 -> 1/28...
    if (x_offset < x_shift / 4) {
        x_offset = x_shift / 2;
    } else {
        x_offset = 0.0;
    }   
}

const int numAtoms = atoms.size();
//print the position of each atom in the file init.dat
for (int i = 0; i < numAtoms; i++) {
    myfile << "x is " << atoms[i].pos.x << " y is " << atoms[i].pos.y << endl;
}

myfile.close();
}

第2部分：能源计算

vector<Atom> atoms;
BoxData box_;

void SystemEnergy()
{
ofstream myfile("energy.dat", ios::out);

double box_Len, box_LenHalf, box_d0;
double dij; // distance between two atoms
double Uij; // energy between two particles
double UTotal = 0;
double pbcx, pbcy; // pbc -> periodic boundary condition
double dx, dy;

myfile << "d0 is " << box_d0 << endl;

// define the number of atoms as the size of the array of atoms
const int numAtoms = atoms.size();

//pick atoms
for (int i=0; i<numAtoms-1; i++) { // pick one atom -> "Atom a"
    Atom &a = atoms[i];
    for (int j=i+1; j<numAtoms; j++) { // pick another atom -> "Atom b"
        Atom &b = atoms[j];

        dx = a.pos.x - b.pos.x;
        dy = a.pos.y - b.pos.y;
        pbcx = 0.0;
        pbcy = 0.0;

        // enforce periodic boundary conditions
        if(dx >  box_LenHalf) pbcx =- box_Len; 
        if(dx < -box_LenHalf) pbcx =+ box_Len;
        if(dy >  box_LenHalf) pbcy =- box_Len;
        if(dy < -box_LenHalf) pbcy =+ box_Len;
        dx += pbcx;
        dy += pbcy;

        // calculate distance between atoms
        dij = sqrt(dx*dx + dy*dy);

        // compare dij to the cutoff distance to determine energy           
        if (dij > box_d0) {
            Uij = 0;
        } else {
            Uij = 1;
        }
        myfile << "i is " << i << " j is " << j << " dij is " << dij << " d0 is " << box_d0 << " Uij is " << Uij << endl;
        UTotal += Uij;  // sum the energies
    }
}
myfile << "Energy of the system is " << UTotal << endl;
myfile.close();

}

对于格式化问题感到抱歉 - 将复制/粘贴挂起到论坛。

2D框中的粒子 - 计算能量时的舍入误差

0 个答案: