the second-order optical nonlinearity of crystal 3-methoxy-4-hydroxy- benzaldehyde (MHBA0 was studied by using the finite field method at the MP2 level with basis set of 6-31G+(p,d). The theoretical results of d~2~1, d~2~2, d~2~3 and d~2~5 were in agreement with the experimental data. The eletron-accepting group HC＝O and the electron-donating group HO played important roles in the nonlinear optical property of MHBA. The results also showed that the hydrogen bonds did not contribute signifcantly to the crystal nonlinear optical coefficients.

Key words: VANILLIN, NON-LINEAR MATERIALS, BENZALDEHYDE P, FINITE ELEMENT METHODS