Yes, I can just remove the cat as well and instead do this (based on the NumPy code 3):
# NumPy fft.fftfreq in PyTorch
def pytorch_fftfreq(n, d=1.0, device='cpu'):		
    results = torch.empty(n, device=device)
    s = (n-1) // 2 + 1
    results[:s] = torch.arange(0, s, device=device)
    results[s:] = torch.arange(-(n//2), 0, device=device)
    return results * (1.0 / (n * d))