import type { VacfInput, VacfOptions, VacfResult } from './index';
export declare const VACF_FREQUENCY_UNITS: readonly ["THz", "cm^-1", "1/frame"];
export declare function central_difference_velocities(positions: Float64Array, n_frames: number, n_atoms: number, dt: number): Float64Array;
export declare function autocorrelation_sums(velocities: Float64Array, n_frames: number, n_atoms: number, atom_group: Int32Array, n_groups: number, max_lag: number): Float64Array[];
export declare function calc_vacf(input: VacfInput, options?: VacfOptions): VacfResult;