Multi-configurational Time Dependant Hartree (MCTDH)
Nicholas J. Browning
Contents
-
Time Dependant Picture
-
Standard Method (SM)
-
Variational Principle (VP)
-
SM Equations of Motion (EoM)
-
Pitfalls of SM
-
-
Multi-configurational TDH (MCTDH)
- MCTDH EoM
- MCTDH Memory Requirements
- MCTDH Numerical Effort
- MCTDH Limitations
- MCTDH Mode Combination
- MCTDH Example
Time Dependant Picture
(TI) orthonormal basis functions
Goal: derive equations of motion for coefficients
the Standard Method
nuclear coordinates or DoF
TD expansion coefficients
number of basis functions for DoF k
number of DoF
Variational Principle
Dirac-Frenkel Variational Principle
SM Equations of Motion
Pitfalls of the Standard Method
Need at least 10 basis functions
per degree of freedom
coupled equations to be solved
E.g. 6 atom molecule
Time Dependant Hartree (TDH)
constraints:
variation in
variation in
TDH EoM
choice of gk is arbitrary - simply shifts phase factors between a and \psi_k
TDH Pitfalls
TDH reduces an f-dimensional PDE to a set of f one-dimensional PDEs
SM
TDH
visualisation of v - <v>
MCTDH
MCTDH
DFVP
MCTDH - Memory
f | Standard Method | MCTDH | |||
---|---|---|---|---|---|
3 | 1.54MB | 190KB | 343 | 672 | 32768 |
4 | 48MB | 620KB | 2401 | 896 | 1.05E+06 |
6 | 48GB | 22MB | 117E+03 | 1344 | 1.07E+09 |
9 | 1.54PB | 7.2GB | 40E+06 | 2016 | 3.5E+13 |
n=7, N=32
MCTDH - CPU EFFORT
Limiting factor for both memory and CPU is A-vector length
MCTDH - Limitations
MCTDH - Mode Combination
MCTDH-MC Pictoral Representation
a) Standard method
b) MCTDH
c) MCTDH with Mode Combination
d) ML-MCTDH (3 layer)
e) ML-MCTDH (4 layer)
MCTDH Mode Combination - Memory
f | St. Method | MCTDH | 2-mode MCTDH | 3-mode MCTDH |
---|---|---|---|---|
2 | 48KB | 282KB | - | - |
4 | 48MB | 620KB | 6MB | - |
6 | 48GB | 22MB | 10MB | 290MB |
10 | 48PB | 51GB | 160MB | 310MB |
15 | - | - | 210GB |
|
18 | - | - | 7.38TB | 29.3GB |
Example: Butatriene PhotoIonisation
C. Cattarius, G. A. Worth, H. D. Meyer, L. S. Cederbaum, J. Chem. Phys, 115 (2001), 2088-2100.
18f, 2 electronic states
Thanks.
MCTDH
By Nick Browning
MCTDH
- 913