The standard pairwise interaction calculation in MD leads to an O ( N 2 ) complexity for N particles. This is because each particle interacts with every other particle, resulting in N ( N − − 1 ) 2 interactions. Advanced algorithms, such as the Ewald summation or Fast Multipole Method, reduce this to O ( N log ⁡ ⁡ N ) or even O ( N ) by grouping distant particles and treating them as a single entity or using clever mathematical approximations.