Sample C language program to calculate two-electron atoms (ions).

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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, we first input atomic number Z = 2, 3, 4, 5, 6, 7, 8, 9, or 10.
Next we input the initial x-coordinate r1 (in MM) of electron 1, and the absolute value of the total energy E (in eV) of two-electron atoms (ions).
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 Z,r,E,nucle,nuclee,rm,Ene;
   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;  
  
                                  /* input Z,  r1 and |E| */

   printf("Atomic number Z ? (He=2, Li+=3, Be2+=4, B3+=5, C4+=6, N5+=7...) ");  
   scanf("%lf",&Z);

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

   printf("total energy |E| of two-electron atom (eV) ? ");  
   scanf("%lf", &E);
 
   nucle=2.0*me; nuclee=0.0;
  if (Z == 2 ) { nucle = 6.64465650e-27; nuclee=nucle;}   /* He alpha particle */
  if (Z == 3 ) { nucle = 1.1646e-26; nuclee=nucle;}   /* Li7 nucleus */
   rm=(2.0*me*nucle)/(2.0*me+nuclee); 
   rm=rm*0.5;                                 /* reduced mass ( He, Li ) */

   Ene=-((4.0*Z-1)*(4.0*Z-1)*ele*ele*ele*ele*me)/(64.0*epsi*epsi*h*h);
   Ene=Ene*6.241509e18; 
   printf("Wrong Ene = %.3f\n", Ene);  /* Energy of circular orbit */
 
   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;
   }