﻿ Two electron atom program (C)

### Sample C language program to calculate two-electron atoms.

If you copy and paste the program source code below into a text editor, you can easily compile and run this.
(This program is simple c language, so save this text editor as "filename.c" and compile it.)
In this program, first we input the initial x-coordinate r1 (in MM) of electron 1, and the absolute value of the total energy E (in eV) of helium atom.
From the inputted values, this program outputs the y component of electron 1 velocity after a quarter of its orbit, and WN (the number of de Broglie's waves included in one quarter of the orbital).
Here 1 SS = 1 × 10-23 second and 1 MM = 1 × 10-14 meter.
The initial x-coodinate is automatically increased per calculation until +100.

#include <stdio.h>
#include <math.h>

int main(void)
{
int i;
double r,E,rm;
double vya,vyb,poten,VX,VY,prexx,preyy,WN,ra,rb;
double xx,yy,vk,preVY,preWN,midWN,leng,wav,ac;
double me=9.1093826e-31;
double pai=3.141592653589793;
double epsi=8.85418781787346e-12;
double h=6.62606896e-34;
double ele=1.60217653e-19;
double Z = 2.0;
double nucle = 6.64465650e-27;

rm =(2.0*me*nucle)/(2.0*me+nucle);  /* reduced mass of helium */
rm=rm*0.5;
/* input  r1 and |E| */

printf("r1 between nucleus and electron 1 (MM)？ ");
scanf("%lf",&r);

printf("total energy |E| of helium atom (eV) ? ");
scanf("%lf", &E);

for (i=1; i < 100 ;i++) {      /* repeat until r1=initial r1+100 */

/* poten = potential energy  */
poten=-(2.0*Z*ele*ele)/(4.0*pai*epsi*r)+(ele*ele)/(4.0*pai*epsi*2.0*r);

/* vya= total E-potential energy */
vya=-(E*1.60217646e-19)-poten*1.0e14;
if (vya > 0) {
/* vyb=electron initial velocity (m/sec) */
vyb=sqrt(vya/me);
VY=vyb*1.0e-9;           /* change m/sec to MM/SS */
prexx=r;  VX=0.0; WN=0.0; preyy=0.0;

do {
xx=prexx+VX; yy=preyy+VY;        /* electron 1 position after 1SS */
preVY=VY;preWN=WN ;
vk=VX*VX+VY*VY;
leng=sqrt(vk)*1.0e-14;      /* moving length (m) for 1 SS */
wav=h/(rm*sqrt(vk)*1.0e9);  /* de Broglie wavelength (m)  */
WN=WN+leng/wav;                  /* add de Broglie wavelength */
/* calculation of VX,VY from Coulomb force  */
ra=sqrt(prexx*prexx+preyy*preyy);  /* between nucleus and electron  */
rb=sqrt(4.0*prexx*prexx+2.0*preyy*preyy); /* between two electrons  */

ra=ra*1.0e-14; rb=rb*1.0e-14;    /* change MM to meter  */
prexx=prexx*1.0e-14; preyy=preyy*1.0e-14;
ac=(ele*ele)/(4.0*pai*epsi*rm);
/* acceleration (MM/SS^2) */
VX=VX+1.0e-32*ac*prexx*(-Z/(ra*ra*ra)+2.0/(rb*rb*rb));
VY=VY+1.0e-32*ac*preyy*(-Z/(ra*ra*ra)+1.0/(rb*rb*rb));
prexx=xx;preyy=yy;

} while (xx >= 0);              /* electron has moved one quater of an orbit? */
if (VY > -0.0001 && VY < 0.0001) {    /* last VY condition */

printf("r1= %.2f ", r );
printf("VX= %.6f ", VX);
printf("VY= %.6f ", VY);
printf("preVY= %.6f ", preVY);
midWN=(preWN+WN)/2.0; printf("midWN= %.6f\n", midWN);
}
}  r=r+1;
}  return 0;
}