RevRelax

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Why Use This Engine?

Most of an optimization’s cost goes into getting close to the right geometry, which a cheap method does well. Only the last steps and the energy need an accurate one. RevRelax passes each structure through a sequence of methods, each starting from the geometry the previous one produced, then scores the result once with a more accurate method still. That gives close to the accuracy of the expensive method at a fraction of its cost. Use it to clean up a drawn or generated structure before another calculation, to get energies for a set of molecules at one level of theory, to confirm with frequencies that a structure is a true minimum and get its free energy, or to refine a guessed transition state.

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Background

Each preset fixes the optimization stages and the final energy method. The level of theory reads right to left: optimization starts with the rightmost method, and the leftmost gives the final single-point energy.

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How It Works

When a minimum comes out with an imaginary vibration, RevRelax pushes the structure along it and optimizes again, up to 3 times. Constrained structures are optimized once. A solvent applies to the final energy, and to the optimization stages as well when Optimize in the solvent too is on. xTB stages use ALPB while optimizing and CPCM-X for a final energy. DFT stages use C-PCM. GFN-FF always runs in the gas phase. Transition-state mode starts from your guess, so the guess must already be close to the saddle point. It runs with Rapid, Careful and Meticulous.

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Running the Engine

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Inputs

A SMILES gives one 3D shape, which RevRelax refines to the nearest minimum. That minimum may sit above the lowest-energy conformer; run RevConformer first to find the lowest. A SMILES holding more than one molecule, such as a salt, is listed as failed with the reason; submit each component on its own. Up to 50 molecules per run, from files up to 10 MB, with elements H to Rn. Molecules can have up to 200 atoms with Reckless and Rapid, 100 with Careful and 40 with Meticulous, counting hydrogens. A larger molecule is refused at submission, with its position in the input and the limit.

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Outputs

The results table lists one row per molecule in input order, with its status and final energy. When frequencies are computed, it also shows the free energy and the number of imaginary vibrations. A count other than 0 for a minimum, or 1 for a transition state, is highlighted. Select a molecule to see each stage’s energy, steps and convergence, its frequencies, any notes, and the structure in 3D. A molecule that fails, from an unreadable SMILES, a charge and multiplicity that do not fit, or a failed optimization, is listed with its reason, and the other molecules carry on. One that failed part-way shows the last structure it reached. Download gives one zip with these files:

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Reading the Result

Energies are absolute, in Hartree. Compare them between structures with the same atoms, such as conformers, isomers, or a reactant and its transition state, run with the same preset. A minimum that still has an imaginary vibration after 3 pushes is flagged in its notes. The Imaginary column shows how many pushes were needed. A constrained structure stays fixed along its held coordinates, so imaginary vibrations along them are expected, and its free energy is left out. A transition state should have exactly one, and any other count is noted. A stage that reaches its step limit before converging is noted, and the next stage continues from where it stopped. When that was the last stage, the final structure may need more steps to settle.

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Interactive Results Viewer

Two worked examples. Ibuprofen is run with every preset from the same starting structure: Reckless, Rapid and Careful each optimize it in one stage, and Meticulous in two, with r²SCAN-D4/vDZP and then ωB97X-3c. The Claisen rearrangement is a transition-state search from one guess with Rapid and with Careful, and both end with exactly one imaginary vibration, at 494i cm⁻¹ and 438i cm⁻¹. Pick an example, then a preset, and switch the 3D view between the input, each stage’s structure and the final structure.