Parallelise nested for loop where inner depends on outer with OpenMP

Question

I have a function in C which I have to parallelize using OpenMP with static scheduling for n threads

void resolveCollisions(){
    int i,j;
    double dx,dy,dz,md;
    for(i=0;i<bodies-1;i++)
        for(j=i+1;j<bodies;j++){
            md = masses[i]+masses[j];
            dx = fabs(positions[i].x-positions[j].x);
            dy = fabs(positions[i].y-positions[j].y);
            dz = fabs(positions[i].z-positions[j].z);
            if(dx<md && dy<md && dz<md){
                vector temp = velocities[i];
                velocities[i] = velocities[j];
                velocities[j] = temp;
            }
        }
}

So in order to parallelize this I added a #pragma omp parallel for directive to parallelize the outer loop across the n threads. I also added the static scheduling tag which I have to use. I also put the num_threads(n) which takes the n from the function parameters to know the desired number of threads. I also thought about adding a critical section to prevent race conditions when updating the velocities array.

void resolveCollisions_openMP-static(int n) {
    int i, j;
    double dx, dy, dz, md;
    #pragma omp parallel for schedule(static) num_threads(n)
    for (i = 0; i < bodies - 1; i++) {
        for (j = i + 1; j < bodies; j++) {
            md = masses[i] + masses[j];
            dx = fabs(positions[i].x - positions[j].x);
            dy = fabs(positions[i].y - positions[j].y);
            dz = fabs(positions[i].z - positions[j].z);
            if (dx < md && dy < md && dz < md) {
                vector temp = velocities[i];
                #pragma omp critical
                {
                    velocities[i] = velocities[j];
                    velocities[j] = temp;
                }
            }
        }
    }
}

When I run this function though it gives me wrong results. I imagine that it has something to do with the inner loop using i, in order to give value to j in j=i+1. I don't know how to approach to fix this or if this is the actual issue or if it's not. I would appreciate any help. Thank you