From 2c9ac27c505feda1c62bee3f875d52e2e575f35c Mon Sep 17 00:00:00 2001 From: Qi Zhang Date: Tue, 21 Aug 2018 19:30:45 -0400 Subject: [PATCH] fix: Update README.md --- README.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/README.md b/README.md index 6c13259..4a89250 100644 --- a/README.md +++ b/README.md @@ -3,7 +3,7 @@ A crystalline structure is stable, in the absence of external load and in the harmonic approximation, if and only if 1. all its phonon modes have positive frequencies for all wave vectors (dynamical stability); -2. the elastic energy is always positive. This condition is called the *elastic stability criterion*. As first noted by Born (See Ref. 2), it is mathematically equivalent to the following necessary and **sufficient stability conditions**: +2. the elastic energy is always positive. This condition is called the *elastic stability criterion*. As first noted by Born (See Ref. 2), it is mathematically equivalent to the following **necessary and sufficient stability conditions**: 1. The matrix $\mathrm{ C }$ is definite positive; 2. all eigenvalues of $\mathrm{ C }$ are positive; 3. all the leading principal minors of $\mathrm{ C }$ (determinants of its upper-left $k \times k$ submatrix, where $1 \le k \le 6$) are positive, a property known as *Sylvester’s criterion*;