open-standards/wai/wai-quantum/examples/chem_dmrg.rs

//! A molecule's ground state by DMRG from its FCIDUMP integrals, against
//! Hartree–Fock and, where it fits, full configuration interaction.
//!
//! ```text
//! cargo run --release --example chem_dmrg --features quantum_chem -- FILE BOND SWEEPS [threads]
//! ```
use wai_quantum::quantum_chem::{fci, ground_state, hartree_fock_energy, molecular_mpo, read_fcidump, ChemConfig};

fn main() {
    let a: Vec<String> = std::env::args().collect();
    let fd = read_fcidump(&std::fs::read_to_string(&a[1]).expect("read the FCIDUMP")).expect("parse the FCIDUMP");
    let bond: usize = a[2].parse().unwrap();
    let sweeps: usize = a[3].parse().unwrap();
    let mut cfg = ChemConfig { max_bond: bond, sweeps, ..ChemConfig::default() };
    if let Some(t) = a.get(4) {
        cfg.threads = t.parse().unwrap();
    }
    let mpo = molecular_mpo(&fd, &cfg);
    println!("{}: {} orbitals, {} electrons, MPO bond {}", a[1], fd.norb, fd.nelec, mpo.max_bond());
    println!("Hartree–Fock  {:.10}", hartree_fock_energy(&fd));
    let t0 = std::time::Instant::now();
    let r = ground_state(&fd, &cfg);
    let secs = t0.elapsed().as_secs_f64();
    for (i, e) in r.sweep_energies.iter().enumerate() {
        println!("sweep {:>2}      {e:.10}", i + 1);
    }
    println!("discarded     {:.1e}   entropy, mid {:.4}   {secs:.1}s", r.discarded, r.entropies[r.entropies.len() / 2]);
    let t0 = std::time::Instant::now();
    match fci(&fd) {
        Some(f) => println!("full CI       {:.10}   ({} determinants, {:.1}s)   DMRG − full CI {:.2e}", f.energy, f.dim, t0.elapsed().as_secs_f64(), r.energy - f.energy),
        None => println!("full CI       (too large)"),
    }
}