Segmentation fault; rule of three

I have a header file like this

#ifndef __coulomb_h_
#define __coulomb_h_
#include "nml_dcvector.h"
#include <fstream>
#include <iostream>
#include <complex>

#include <vector>
using namespace std;

class Coulomb{

public:

 typedef complex<double> Complex_t;


 Coulomb(int na, int g1, int g2, int o)
  : numAtoms(na), g_min(g1), g_max(g2), o_max(o)
  {

   o_total=o_max*o_max;

   _H_coul = new complex<double>[1];
   _H_exch = new complex<double>[1];

  }

private:

  complex<double>* _H_coul;
  complex<double>* _H_exch;

Then in my .cpp file I write this line

Coulomb nishat = Coulomb (int a, int b, int c, int d)

which is giving segmentation fault. I guess it is due to rule of three . Then I have added this part;copy constructor and assignment constructor

Coulomb (const Coulomb& v):numAtoms(v.numAtoms), g_min(v.g_min),          
 g_max(v.g_max), o_max(v.o_max) 
{
 o_total= v.o_total;

_H_coul = new complex<double>[1];

_H_exch = new complex<double>[1];

 }

 Coulomb& operator= (const Coulomb& v)

  {

  int o_total= v.o_total;

  complex<double>* _H_coul_temp = new complex<double>[1];

  std::copy(v._H_coul,v._H_coul+1, _H_coul_temp  ) ;

    complex<double>* _H_exch_temp = new complex<double>[1];

   std::copy(v._H_exch,v._H_exch+1, _H_exch_temp  );

  delete [] _H_coul; delete [] _H_exch;

  _H_coul= _H_coul_temp;

  _H_exch= _H_exch_temp;

  return *this; 

  }

 Still not working. Please anybody help me to resolve this problem. thanks