typedef struct particle PARTICLE;
struct particle
{
    unsigned int idparticle;
    double pos[D];
    double vel[D];
    double force0[D];
    double force[D];
    double mass;
    char bf[BFSIZE];
    void *nxtParticle;
};
PARTICLE particle[(int) N];
PARTICLE *particles;
...
for(i=0;i<N;i++){
   particle[i].nxtParticle=(i==N-1)?NULL:&particle[i+1];
   particle[i].idparticle=i;
}