The Fastest Way to Accurate Quantum Chemical Energies

Sometimes compromises with respect to accuracy might be acceptable. Sometimes it might be sufficient to just hopefully get the trends right.

But most of the time you want to calculate numbers that are correct and trustworthy. And, most of the time, you don't have time on your hands to wait for these numbers.

This is were DLPNO-CCSD(T) steps in:

DLPNO-CCSD(T) is the fastest – and easiest – way to quantum chemical energies that you can trust.

What can you expect from DLPNO-CCSD(T)?

CCSD(T) results are widely accepted as the gold-standard in quantum chemistry. DLPNO-CCSD(T) is an approximation to this standard that is

  • highly accurate, i.e. it recovers 99.9% of the CCSD(T) correlation energy
  • super fast, i.e. its computational cost is similar to DFT and scales linearly with system size
  • easy to use, i.e. it operates black box with zero need to adjust parameters.

DLPNO-CCSD(T) is the sole method that combines near-CCSD(T) accuracy with DFT speed in an easy-to-use black-box fashion.

DLPNO-CCSD(T) – Too Good to be True?

A method that overcomes the compromise between speed and accuracy: Does this sound too good to be true?

There's no need to believe in empty words. DLPNO-CCSD(T) underwent multiple benchmarks and they consistently confirm its performance.

Don't just take our word for it — find out for yourself.

As Accurate As It Gets: 99.9% of CCSD(T)

DLPNO-CCSD(T) energies are accurate: They reproduce more than 99.9% of the CCSD(T) correlation energy.

 Show Me Proof

As Fast As It Gets: near-DFT Cost

DLPNO-CCSD(T) energies are calculated fast: Their computational cost is 2–4 times the cost of a DFT calculation.

 Show Me Proof

As Easy As It Gets: Single Keyword Access

DLPNO-CCSD(T) energies are calculated easily: Simply specify the keyword DLPNO-CCSD(T) in the input keyword line.

 Show Me How


DLPNO-CCSD(T) is the fastest — and easiest — way to highly accurate energies.

  1. It recovers more than 99.9% of the CCSD(T) energy.
  2. It scales linearly.
  3. It operates black box with a single keyword.

Plus: It is embedded in a powerful quantum-chemical software Suite — ORCA.

Have Fun with ORCA!

Discover More

We do not stop at closed-shell, single-point energies, however. Profit from DLPNO-CCSD(T) speed and accuracy in

  • Multi-Level Schemes
  • Local Energy Decomposition
  • Embedding Schemes for Solids
  • Easy Integration into QM/MM
  • Open-Shell Energies
  • Density/Properties
  • Excited States
  • Combination with Implicit Solvation Models (available soon)