(* C3H8 Molekül nach Kimball, nicht überlappend,
     parametrisiert mit G2//6-311g *)

  Clear[k1,k2,k3,s1,s2,s3];  n=3.;

  (* Terme automatisch mit ChemEdu/Kimball/Alkan.sys *)

  T=2.25*n*k1/P^2+(n-1.0)*2.25*k2/Q^2+4.5*(n+1.0)*k3/R^2; 
  
  p=X;  p2=p*p;  q=P+Q;  r=P+R;  q2=q*q;  r2=r*r;  
  r2p2=r2*p2;  r2p=r2*p;  qr=q*r; qrp=qr*p; z=6.; z2=z*z;  
  dd=32.0/3.0;  cd=19.0/3.0;  sd=16.0/3.0;
  jd=10.0/3.0;  ad=8.0/3.0;  vd=4.0/3.0;  zd=2.0/3.0;

  Vne = -3.0*n*z/P-2.0*(n+1.0)*(3.0-((p-1.0)*(1.0+P/R))^2)/R-
        16.0*z/r -16.0/r/p-8.0*z/2.0/q-
        20.0*z/Sqrt[vd*qr+4.0*q2+r2]-
        20.0/Sqrt[vd*qrp+r2p2+4.0*q2]-8.0*z/Sqrt[q2]-
        28.0/Sqrt[zd*r2p+r2p2+r2]-
        32.0/Sqrt[vd*qr+vd*qrp-zd*r2p+r2p2+4.0*q2+r2]-
        16.0/Sqrt[vd*qr+vd*qrp+2.0*r2p+r2p2+4.0*q2+r2]-
        20.0/Sqrt[zd*qrp+r2p2+q2]-4.0*z/Sqrt[dd*q2]-
         8.0*z/Sqrt[dd*q2+r2]-8.0/Sqrt[r2p2+dd*q2]-
         4.0*z/Sqrt[cd*q2]-4.0*z/Sqrt[sd*qr+dd*q2+r2]-
         4.0/Sqrt[sd*qrp+r2p2+dd*q2]-
         8.0/Sqrt[zd*r2p+r2p2+dd*q2+r2]-
         8.0/Sqrt[-2.0*r2p+r2p2+dd*q2+r2]-
         8.0/Sqrt[sd*qrp+zd*r2p+r2p2+dd*q2+r2]-
         8.0/Sqrt[zd*qrp+r2p2+cd*q2]-
         8.0/Sqrt[sd*qr+zd*r2p+r2p2+dd*q2+r2]-
         4.0/Sqrt[jd*qrp+r2p2+cd*q2]-
         4.0/Sqrt[sd*qr+sd*qrp+zd*r2p+r2p2+dd*q2+r2];

  Vee =   3.0*n*s1/P+(n-1.0)*3.0*s2/Q+(n+1.0)*6.0*s3/R+32.0/r+
          8.0/2.0/q+40.0/Sqrt[vd*qr+4.0*q2+r2]+16.0/q+
         28.0/Sqrt[ad*r2]+32.0/Sqrt[ad*qr+4.0*q2+vd*r2]+
         16.0/Sqrt[ad*qr+4.0*q2+4.0*r2]+40.0/Sqrt[zd*qr+q2+r2]+
         12.0/Sqrt[dd*q2]+16.0/Sqrt[dd*q2+r2]+8.0/Sqrt[cd*q2]+
          8.0/Sqrt[sd*qr+dd*q2+r2]+8.0/Sqrt[dd*q2+ad*r2]+
         16.0/Sqrt[zd*qr+cd*q2+r2]+16.0/Sqrt[sd*qr+dd*q2+ad*r2]+
          4.0/Sqrt[ad*q2]+8.0/Sqrt[jd*qr+cd*q2+r2]+
          4.0/Sqrt[dd*qr+dd*q2+ad*r2];

  Vnn =   8.0*z/r/p+2.0*z2/2.0/q+10.0*z/Sqrt[vd*qrp+r2p2+4.0*q2]+
          7.0/Sqrt[ad*r2p2]+8.0/Sqrt[ad*qrp+vd*r2p2+4.0*q2]+
          4.0/Sqrt[ad*qrp+4.0*r2p2+4.0*q2]+2.0/Sqrt[dd*q2]+
          z2/Sqrt[dd*q2]+4.0*z/Sqrt[r2p2+dd*q2]+
          2.0*z/Sqrt[sd*qrp+r2p2+dd*q2]+2.0/Sqrt[ad*r2p2+dd*q2]+
          4.0/Sqrt[sd*qrp+ad*r2p2+dd*q2]+
          1.0/Sqrt[dd*qrp+ad*r2p2+dd*q2];

  func=T+Vne+Vee+Vnn;

  (* Parameterliste c *)

  c={k1 -> 1.02248824, k2 -> 1.37439662, k3 -> 1.20536809, 
  s1 -> 0.30582289, s2 -> 0.30680633, s3 -> 0.35440675 };

  func = func /. c;

  N[t = FindMinimum[func, {P,0.26134285}, {Q, 1.18367097}, 
                          {R, 1.2729},{X, 1.356986}], 10]

u  =  t[[2]];
N[Vne  /.  u, 10]

N[Vee  /. u  /. c, 10]

N[Vnn  /. u, 10]

ch = X*(P + R)  /. u;
dch = ch*0.529177

cc = 2. *(P + Q)  /. u;
dcc = cc*0.529177

N[-(Vne + Vee + Vnn)/T  /. u  /. c,  
      10]

(-t[[1]] - n*37.784301 - n - 
          1.0)*627.50956