Q-Chem 4.0: Expanding the Frontiers Jing Kong Q-Chem Inc. Pittsburgh, PA
Q-Chem: Profile Q-Chem is a high performance quantum chemistry program; Contributed by best quantum chemists from 40 universities worldwide, including Berkeley, MIT, USC, Tubigen, ANU; Led by Board: Head-Gordon, Gill, Schaefer, Krylov, Pople, Kong.
Q-Chem: Notables 1997: First version Q-Chem 1.0: first linear-scaling DFT with continuous fast multiple method; 1999: Prof. John Pople joined Q-Chem after winning Nobel Prize; 2002: New Spartan with Q-Chem as the back end engine; Eight releases in the last 11 years; Last release: Q-Chem 3.2; Happening Now: Q-Chem 4.0.
Q-Chem 3.0 Paper Advances in methods and algorithms in a modern quantum chemistry program package Physical Chemistry Chemical Physics Vol 8, 3172 (2006) 66 authors worldwide 37 institutes
Quantum Chemistry Methods Hierarchy of Methods HF: low accuracy, clear phys. Picture; MP2: accurate for equalibrium structures, weak interactions; Coupled clusters: very accurate, high cost; Multireference methods: even more expensive; DFT: accurate, low cost, picture less clear, a bit empirical.
Quantum Chemistry Methods Challenges for Method Developers Computational cost: speed, memory; Nondynamic correlation: transition state, bond stretching, multiple-bonds, transition metals, radicals; Weak interactions: dispersion, H-bonding; Real (read Large ) systems; Fundamentally, how to make predictions accurate enough with what we have;
Density Functional Theory The accuracy of DFT is determined by the exchangecorrelational functional used; Q-Chem has almost all the conventional functionals: B3LYP, BMK, M06-2X; Deficiencies of Conventional Functionals No dispersion; Self-interaction error; Fail on static correlation.
DFT: Dispersion Solutions in Q-Chem for Dispersion MM-like empirical formulism: Grimme s DFT-D, DFT-D3, Q-Chem s wb97x-d; Electronic: DF-vdW, XDM; Add MP2 to DFT.
DFT: Dispersion Exchange Dipole Moment (XDM) Proposed by Becke and Johnson Electronic model with few parameters We made efficient implementation in SCF O O CH 3 ccpvtz Basis E eq -E ax (kcal/mol) O B3LYP 0.63 (-0.12) CCSD(T) 1.47 (0.49) B3LYP+XDM 1.07 (0.32) O Experiment (0.47 ± 0.3) CH 3
Enegy (kcal/mol) Energy (kcal/mol) DFT: Dispersion Mix DFT with MP2 Parameterization similar to mixing DFT with HF; An example: XJGS-OS; Improve both the long-range and short-range. 1.50 B3LYP H + CH 4 H 2 + CH 3 21.00 1.00 0.50 0.00 MP2 XYG3 XYGJ-λOS CCSD(T) 18.00 15.00 12.00 B3LYP MP2 XYG3 XYGJ-λOS CCSD(T) 3.00 3.50 4.00 4.50 5.00 5.50 6.00-0.50 9.00-1.00 6.00-1.50-2.00-2.50 CH 4 -C 6 H 6 3.00 0.00-2.00-1.00 0.00 1.00 2.00 Reaction coordinate
DFT: Speed Q-Chem Has Some of the Best DFT Algorithms Continuous fast multipole, the first linear-scaling Coulomb in quantum chemistry; J-engine makes Coulomb fast for even small molecules; More recently Fourier transform Coulomb; LinK the linear-scaling HF exchange; All without error!
New DFT Algorithms in 4.0 Multiresolution Exchange-Correlation (mrxc) Basis set XC is a major part of DFT calculation Compact density on atom-centered grid Smooth density on even-spaced grid Super fast with no errors Example: taxol with BLYP (113 atoms) # of basis functions Errors 10-6 a.u./atom Speed-up Speed-up with FTC a 6-31G(df,pd) 1925 0.03 3.9 5.0 cc-pvtz 2574 0.1 5.8 9.6
New DFT Algorithms in 4.0 Large Basis Calculation at the Cost of Small Basis Do SCF with the small basis Do one projection step to the large basis 10 times faster DFT, HF, MP2 energy and gradient G2 database thermochemistry with B3LYP in kcal/mol. Small basis single basis dual basis 6-311G MAD = 24.3 MAD = 4.0 6-311G* MAD = 7.0 MAD = 2.2 6-311++G(3df,3pd) MAD = 2.2 MAD = 2.2
NMR Chemical Shifts O(N) NMR Chemical Shifts Build on LinK and O(N) Coulomb Using sparse-matrix techniques Can treat much larger system than before
NMR Chemical Shifts
DFT Speed: Accelarate with GPU XC on GPU (Graphic Processing Unit) Take advantage of BLAS Achieve very good performance: 60% of peak performance Example: Tesla: 960 cores@1.45ghz, Peak 312 Gflops CPU: Quad core Xeon @ 2.8GHz, Peak 44.8Gflops
Hybrid Computing
DFT: More Other DFT Features Parallel frequency calculation with shared memory; TDDFT energy, gradient, and Hessian.